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1500 Cards in this Set

  • Front
  • Back
what are prions composed of?
abnormal forms of a host protein called prion protein (PrP)
with what is kuru associated?
human cannibalism
what are the prion diseases?
creutzfeldt-jakob disease (CJD)
bovine spongiform encephalopathy (BSE/mad cow disease)
variant creutzfeldt-jakob disease
how is variant creutzfeldt-jakob disease transmitted to humans?
from BSE-infected cattle
what is PrP?
prion protein

abnormal form of host protein that composes prions

normally found in neurons
where is PrP usually found?
what change occurs in PrP, causing prion diseases?
conformational change that renders it resistant to proteases

protease-resistant PrP promotes the conversion of normal protease-sensitive PrP to the abnormal form
how can creutzfeldt-jakob disease be transmitted from person to person?
by surgery
organ transplant
blood transfusion
define iatrogenic
an inadvertent adverse effect or complication resulting from medical treatment or advice, including that of psychologists, therapists, pharmacists, nurses, and dentists
obligate intracellular parasites

use host cellular machinery to replicate

consist of a nucleic acid genome surrounded by a protein coat (capsid), and sometimes encased in a lipid membrane (envelope)
what inclusions are produced by cytomegalovirus?
large eosinophilic nuclear inclusion

smaller basophilic cytoplasmic inclusions
what inclusions are produced by herpesviruses?
large nuclear inclusion surrounded by a clear halo
what is a latent infection?
a nonreplicating form of viral infection, where the virus survives in a dormant form with the potential to be reactivated later

e.g. herpes zoster virus (chickenpox and shingles)
describe the latent infection with herpes zoster virus
infects and causes chickenpox in childhood

enters dorsal root ganglia and establish latency

in adult life, is periodically activated to cause shingles (not in everyone)

have a cell membrane, but no membrane-bound organelles; surrounded by a wall of peptidoglycan

can be extracellular, facultative intracellular, or obligate intracellular
how do prokaryotes differ from eukaryotes?
both have cell membranes

eukaryotes have membrane-bound organelles, but prokaryotes do not
surface projections in bacteria that can adhere to host cells or extracellular matrix
what is the difference in peptidoglycan between gram-positive and gram-negative bacteria?
gram-positive bacteria have a thick wall of peptidoglycan surrounding the cell membrane that retains crystal-violet stain

gram-negative bacteria have thin peptidoglycan walls sandwiched between two phospholipid bilayer membranes
where are both staphylococcus epidermidis and propionibacterium acnes typically found to colonize?
what bacteria causes acne?
propionibacterium acnes
what is the major contributor to dental plaque?
aerobic and anaerobic bacteria in the mouth, particularly streptococcus mutans
define microbiome
the totality of microbes, their genetic elements (genomes), and environmental interactions in a defined environment
give examples of obligate intracellular bacteria
chlamydia (epithelial cells)
rickettsia (endothelial cells)

replicate in membrane-bound vacuoles in specific cells identified

get most/all of their energy from host cell
what is the most frequent infectious cause of female sterility?
chlamydia trachomatis

causes scarring and narrowing of the fallopian tubes
what is the most frequent infectious cause of blindness?
chlamydia trachomatis

causes chronic inflammation of the conjunctiva that eventually causes scarring and opacification of the cornea
what generic diseases are caused by rickettsiae?
injure endothelial cells, causing a hemorrhagic vasculitis, often visible as a rash

injure CNS & cause death (rocky mountain spotted fever; epidemic typhus)
how are rickettsiae transmitted?
arthropod vectors

lice (epidemic typhus)
ticks (rocky mountain spotted fever; ehrlichiosis)
mites (scrub typhus)
how are mycoplasma and ureaplasma unique among extracellular bacterial pathogens?
do not have a cell wall

tiniest free-living organisms known (125-300nm)

thick chitin-containing cell walls; ergosterol-containing cell membranes
what is thermal dimorphism?
ability of some fungi to change form depending on the temperature

"mold in the cold" - slender filamentous hyphae outside the body
"yeast in the heat" - rounded yeast cells inside the body
what are the two types of spores produced by fungi?
sexual spores

asexual spores (aka conidia)
what are conidia?
asexual spores of fungi

produced on specialized fruiting bodies arising along the hyphal filament
what are dermatophytes?
fungal species whose infections are confined to the superficial layers of the skin
where is coccidioides geographically restricted to?
southwestern united states
where is histoplasma geographically restricted to?
ohio river valley
what is the effect of opportunistic fungi on immunocompromised individuals?
give rise to life-threatening infections

characterized by tissue necrosis, hemorrhage, and vascular occlusion, with little/no inflammatory response
what fungus commonly infects AIDS patients?
pneumocystis jiroveci (formerly called pneumocystis carinii)
single-celled eukaryotes

major cause of disease and death in developing countries

intracellular replication in variety of tissues or extracellular in the urogenital system, intestine, or blood
in what type of cells does Leishmania replicate?
what are the most prevalent intestinal protozoans?
entamoeba histolytica

giardia lamblia
what are the two forms of entamoeba histolytica?
motile trophozoites (attach to intestinal epithelial wall and may invade)

immobile cysts (resistant to stomach acids and infectious when ingested)
what are the two forms of giardia lamblia?
motile trophozoites (attach to intestinal epithelial wall and may invade)

immobile cysts (resistant to stomach acids and infectious when ingested)
how are blood-borne protozoans transmitted? give some examples
insect vectors where they replicate before being passed to new human hosts

plasmodium, trypanosoma, leishmania
how is toxoplasma gondii acquired?
contact with oocyst-shedding kittens

eating cyst-ridden, undercooked meat
highly differentiated multicellular organisms

most alternate btwn sexual reproduction in definitive host and asexual multiplication in intermediate host or vector
what happens once adult helminths take up residence in humans?
do not multiply

produce eggs or larvae that are passed out in stool
to what is the severity of helminth-mediated disease proportional?
number of organisms that have infected the individual
what are ectoparasites?
insects (lice, bedbugs, fleas) or arachnids (mites, ticks, spiders) that attach to and live on or in the skin
how do arthropods produce disease?
directly (damaging human host)

indirectly (serving as vectors for transmission of infectious agents)
what causes pediculosis?
lice attached to hair shafts
what is pediculosis?
infestation with lice
what is scabies?
infestation of skin with mites

mites burrow into the stratum corneum
what are the layers of epidermis from outside-in?
stratum corneum
stratum lucidum (only in thick skin)
stratum granulosum
stratum spinosum
stratum basale
what is the malphigian layer?
stratum spinosum and stratum basale as a unit (both considered together)
what can be found at the site of an arthropod bite?
mouth parts associated with a mixed infiltrate of lymphocytes, macrophages, and eosinophils
what is gram staining used for?
most bacteria
what is acid-fast stain used for?
what is silver stain useful for?
what is periodic acid-Schiff useful for?
what is mucicarmine stain useful for?
cryptococci (encapsulated yeast)

stains the capsule
what is giemsa stain useful for?
what are antibody probes useful for identifying?
all classes of microorganisms
what are cultures useful for identifying?
all classes of microorganisms
what are DNA probes useful for identifying?
all classes of microorganisms
where are organisms usually best visualized?
advancing edge of a lesion, particularly if there's necrosis

(not at the center)
what is indicated by the presence of microbe-specific IgM antibodies in the serum shortly after the onset of symptoms?
diagnostic of infection by the specific microbe
how can an infection be diagnosed with antibody titers?
specific antibody titers can be measured early (acute) and 4-6 weeks (convalescent) after infection

four-fold rise in titer is usually considered diagnostic
what are molecular diagnostics?
nucleic acid-based tests for detecting and quantifying various pathogens
treatment of what types of infections is guided by nucleic acid-based measurements?
management of HBV and HCV infections is guided by nucleic acid-based viral quantification/typing

predicts resistance to antiviral drugs
compare PCR testing for herpes simplex virus with cultures in herpes simplex virus encephalitis
PCR testing has a sensitivity of 80%

culture has a sensitivity of less than 10%
what is the manifestation of the ebola virus?
epidemic ebola hemorrhagic fever
what is the manifestation of the hantaan virus?
hemorrhagic fever with renal syndrome
what is the manifestation of legionella pneumophila?
legionnaires disease
what is the manifestation of campylobacter jejuni?
what is the manifestation of human t-lymphocyte virus?
aka HTLV-1

T-cell lymphoma or leukemia
HTLV-associated myelopathy
what is the manifestation of Staphylococcus aureus?
toxic shock syndrome
what are the manifestations of escherichia coli O157:H7?
hemorrhagic colitis
hemolytic-uremic syndrome
what is the manifestation of borrelia burgdorferi?
lyme disease
what is the manifestation of HIV?
aka human immunodeficiency virus

acquired immunodeficiency syndrome (AIDS)
what is the manifestation of helicobacter pylori?
gastric ulcers
what is the manifestation of hepatitis E?
enterically transmitted hepatitis
what is the manifestation of hepatitis C?
hepatitis C
what is the manifestation of vibrio cholerae O139?
new epidemic cholera strain
what is the manifestation of bartonella henselae?
cat-scratch disease
what is the manifestation of HHV-8?
HHV8 = kaposi sarcoma herpes virus

kaposi sarcoma in AIDS
what is the manifestation of west nile virus?
west nile fever
neuroinvasive disease
what is the manifestation of the SARS coronavirus?
severe acute respiratory syndrome
what are the CDC categories for ranking bioweapons?
A - highest risk/most dangerous

B- intermediately dangerous

C - could be engineered to be dangerous
describe category A bioterrorism agents
highest risk

readily disseminated/transmitted

cause high mortality w/ potential for major public health impact

cause public panic and social disruption

require special action for public health preparedness
why is smallpox a category A bioweapon?
easily transmissable in any climate/season

30% mortality rate

lack of effective antiviral therapy
why is smallpox easily disseminated?
it is very stable in aerosol form

a very small dose is needed for infection
how is smallpox naturally spread?
direct contact with virus in skin lesions or contaminated clothing or bedding
what are the symptoms of smallpox infection?
initially - high fever, headache, backache

later - rash (first on mucosa of mouth, pharynx, face, and forearms->trunk and legs) that becomes vesicular and then pustular
when do symptoms of smallpox infection appear?
7-17 days after infection
why is the population susceptible to smallpox infection if there is a vaccine?
vaccination ended in the US in 1972

vaccination immunity has waned
what type of bioweapon is anthrax?
bacillus anthracis

category A
what type of bioweapon is botulism?
clostridium botulinum toxin

category A
what type of bioweapon is yersinia pestis?
aka the plague

category A
what type of bioweapon is smallpox?
variola major virus

category A
what type of bioweapon is francisella tularensis?
causes tularemia

category A
what type of bioweapon are filoviruses?
e.g. ebola and marburg viruses

cause viral hemorrhagic fevers

category A
what type of bioweapon are arenaviruses?
e.g. Lassa and machupo viruses

cause viral hemorrhagic fevers

category A
what type of bioweapon is Brucella sp.?
causes brucellosis

category B
what type of bioweapon is the epsilon toxin of clostridium perfringens?
category B
what type of bioweapon are food safety threats?
e.g. salmonella sp., E. coli O157:H7, shigella

category B
what type of bioweapon is burkholderia pseudomallei?
causes melioidosis

category B
what type of bioweapon is burkholderia mallei?
causes glanders

category B
what type of bioweapon is chlamydia psittaci?
causes psittacosis

category B
what type of bioweapon is coxiella burnetti?
causes Q fever

category B
what type of bioweapon is ricin toxin?
from ricinus communis (castor beans)

category B
what type of bioweapon is staphylococcal enterotoxin B?
category B
what type of bioweapon is rickettsia prowazekii?
causes typhus fever

category B
what type of bioweapon are alphaviruses?
e.g. venezuelan equine encephalitis, eastern equine encephalitis, western equine encephalitis

cause viral encephalitis

category B
what type of bioweapon are water safety threats?
e.g. vibrio cholerae, cryptosporidium parvum

category B
what type of bioweapon is Nipah virus?
category C
what type of bioweapon is Hantavirus?
category C
describe category B bioweapons
moderately easy to disseminate

produce moderate morbidity, but low mortality

require specific diagnostic and disease surveillance

many are food- or water-borne
describe category C bioweapons
emerging pathogens that could be engineered for mass dissemination because of availability, ease of production and dissemination

potential for high morbidity and mortality

potential for great impact on health
what are the first defenses against infection?
intact skin and mucosal surfaces

physical barriers that produce antimicrobial substances
what factors about the skin make it a good first line of defense?
dense, keratinized outer layer of skin
low pH (about 5.5)
presence of fatty acids

inhibit growth of microorganisms other than residents of normal flora
what potential opportunists are normal flora of the skin?
staphylococcus epidermidis
candida albicans
what is infected by dermatophytes?
stratum corneum
how do Schistosoma larvae, released from freshwater snails enter the body?
penetrate swimmers' skin by releasing collagenase, elastase, and other enzymes that dissolve the extracellular matrix
what fungus is commonly found in burns?
pseudomonas aeruginosa
how are most GI pathogens transmitted?
food or drink contaminated with fecal material
what are the normal defenses of the GI tract?
1) acidic gastric secretions
2) viscous mucus layer covering intestinal epithelium
3) lytic pancreatic enzymes and bile detergents
4) defensins
5) normal flora
6) secreted IgA antibodies
what are defensins?
mucosal antimicrobial peptides
where are secreted IgA antibodies made?
plasma cells located in mucosa-associated lymphoid tissues (MALT)
what are M cells?
specialized epithelial cells that cover mucosa-associated lymphoid tissues with a single layer

they transport antigens to the MALT and they bind/uptake numerous gut pathogens
what type of viruses are inactivated by bile and digestive enzymes?
enveloped viruses

nonenveloped viruses may be resistant to bile and digestive enzymes
how do staphylococcal strains cause GI disease?
while growing on contaminated food, they release powerful enterotoxins that cause food poisoning without any bacterial multiplication in the gut
how do V. cholerae and E. coli cause GI disease?
multiply in mucous layer overlying gut epithelium and release exotoxins that cause the gut epithelium to secrete large volumes of fluid, resulting in watery diarrhea
how do shigella, salmonella, and campylobacter cause GI disease?
invade and damage intestinal mucosa and lamina propria

cause ulceration, inflammation, and hemorrhage

clinically manifested as dysentery
how does salmonella typhi cause GI disease?
passes from damaged mucosa, through Peyer patches and mesenteric lymph nodes, and into the blood stream

results in systemic infection
when does fungal infection of the GI tract occur?
mainly in immunologically compromised people
in what form must intestinal protozoans be to infect?
cyst form, because cysts resist stomach acid

convert to motile trophozoites in the gut
how do protozoans infect the intestines?
cysts pass through stomach (they resist stomach acid)

cysts convert to motile trophozoites in gut

trophozoites attach to sugars on intestinal epithelia via surface lectins
what happens to Giardia lamblia when it attaches to sugars on intestinal epithelia?
attaches to epithelial brush border and multiplies there
what happens to cryptosporidia after it attaches to sugars on intestinal epithelia?
taken up by enterocytes, in which they form gametes and spores
what happens to Entamoeba histolytica after it attaches to sugars on intestinal epithelia?
causes contact-mediated cytolysis through a channel-forming pore protein

ulcerates and invades colonic mucosa
when do intestinal helminths cause disease?
present in large numbers

present in ectopic sites
how does Ascaris lumbricoides cause disease?
obstructs the gut

invades and damages bile ducts
how do hookworms cause disease?
cause iron deficiency anemia by chronic loss of blood sucked from intestinal villi
how does Diphyllobothrium latum cause disease?
depletes host of vitamin B12, giving rise to illness resembling pernicious anemia
what is the fish tapeworm?
Diphyllobothrium latum
where do larvae of Trichinella spiralis preferentially encyst?
where do echinococcus species larvae preferentially encyst?
on what is the distance particles travel into the respiratory system dependent?
inversely proportional to size
where are large particles trapped in the respiratory tract?
mucociliary blanket that lines nose and upper respiratory tract
what is the host defense mechanism to particles/microbes that are inhaled?
trapped in mucus secreted by goblet cells

transported by ciliary action to the back of the throat

swallowed and cleared
what happens to particles smaller than 5um?
travel directly to alveoli

phagocytosed by alveolar macrophages or by neutrophils recruited to the lungs by cytokines
what is necessary for microorganisms that invade normal healthy respiratory tract?
must have developed specific mechanisms to overcome the mucociliary defenses or to avoid destruction by alveolar macrophages
what mechanisms have influenza viruses developed to infect respiratory tract defenses?
possess hemagglutinin proteins that project from the surface of the virus and bind to sialic acid on the surface of epithelial cells

host cells are induced to engulf the virus, which enters and replicates within host cells
what mechanisms have influenza viruses developed to exit respiratory tract epithelial cells?
possess neuraminidase proteins on the cell surface, which cleaves sialic acid and allows virus to release from host cell

neuraminidase also lowers viscosity of mucus and facilitates viral transit w/in respiratory tract
why is neuraminidase a good target for anti-influenza drugs?
neuraminidase is a protein on the cell surface of influenza viruses that is essential for cleaving sialic acid so that the virus can leave the cell

some anti-influenza drugs are sialic acid analogues that bind and inhibit neuraminidase and prevent viral release from host cells
what bacteria elaborate toxins that paralyze respiratory mucosal cilia?
Haemophilus influenzae
Bordetella pertussis
what is the major cause of severe respiratory infection in persons with cystic fibrosis?
Pseudomonas aeruginosa
what bacteria produces ciliostatic substances?
M. pneumoniae
how do streptococcus pneumoniae and staphylococcus species infect the respiratory tract, even though they don't have specific adherence factors?
gain access after viral infection causes a loss of ciliated epithelium

individuals with viral respiratory infection are more susceptible to secondary bacterial superinfections
how is the urogenital tract mostly infected?
most urinary tract infections invade from the exterior via the urethra
what is the normal defense against invading microorganisms in the urinary tract?
regular flushing with urine
what microorganisms are usually found in urine of a healthy individual?
a healthy person's urine is usually sterile in the bladder
how do successful urinary tract pathogens infect?
e.g. N. gonorrhoeae, E. coli

adhere to urinary epithelium
why do women have more urinary tract infections than men?
women have more than 10x the urinary tract infections that men have because they have a shorter urethra than men
what is pyelonephritis?
an ascending urinary tract infection that has reached the pyelum or pelvis of the kidney (spread in a retrograde manner from the bladder to the kidney)

major preventable cause of renal failure
what is the presentation of pyelonephritis?
fever, accelerated heart rate, painful urination, abdominal pain radiating to the back, nausea, and tenderness at the costovertebral angle on the affected side
what is the normal defense mechanism of the vagina against microorganisms?
low pH resulting from catabolism of glycogen in the normal epithelium by lactobacilli
why are lactobacilli important to women?
normal flora of the vagina

catabolize glycogen to make lactic acid, which lowers the pH of the vagina, and protects against invading microorganisms
why do women on antibiotics commonly develop vaginal infections?
antibiotics kill the lactobacilli in the vaginal epithelium (normal flora which create the decreased pH by making lactic acid from glycogen) and allowing other bacteria to invade
what bacteria secrete hyaluronidase? what is the effect?
streptococci and staphylococci

degrades the extracellular matrix between host cells so that the bacteria can invade tissues
what viruses are transported free in plasma?
hepatitis B virus
what protozoa are transported free in the plasma?
African trypanosomes
what helminths are transported free in the plasma?
what organisms are transported by leukocytes in the blood?
Leishmania (protozoan)
Toxoplasma (protozoan)
what are secondary foci?
infectious foci seeded by blood

can be:
- single and large (solitary abscess or tuberculoma)
- multiple and tiny (miliary tuberculosis or Candida microabscesses)
what is miliary tuberculosis?
a contagious bacterial (M. tuberculosis) infection that has spread from the lungs to other parts of the body through the blood or lymph system
what are the manifestations of bloodstream invasion by microbes during brushing of teeth?
these microbes are low-virulence or non-virulent

this is common and is quickly controlled by normal host defenses
what are the manifestations of disseminated viremia, bacteremia, fungemia, or parasitemia?

low blood pressure

systemic signs and symptoms of sepsis

can be fatal, even in previously healthy individuals
what are the major manifestations of schistosoma mansoni?
liver and intestinal damage

penetrates through the skin, but localizes in blood vessels of the portal system and mesentery
what are the major manifestations of schistosoma hematobium?

penetrates through the skin, but localizes in the urinary bladder
what are the possible consequences of bacterial or mycoplamal placentitis?
premature delivery

what are the possible consequences of viral infections of a fetus?
maldevelopment of the fetus

infection in early pregnancy results in most severe disease
what are the manifestations of rubella infection during the first trimester? during the third trimester?
first trimester:
- congenital heart disease
- mental retardation
- cataracts
- deafness

third trimester:
- little/no damage
when is Treponema pallidum infection most detrimental to a fetus?
when mother is infected late in the second trimester (this is the only time that T. pallidum infection leads to confenital syphilis), it causes severe fetal osteochondritis and periostitis that leads to multiple bony lesions
what is the major cause of AIDS in children?
maternal transmission of HIV
what is the fecal-oral route of transmission?
ingestion of stool-contaminated food or water

common mode of transmission for viruses, bacteria, protozoans, and helminths
what water-borne viruses are involved in epidemic outbreaks?
hepatitis A virus
hepatitis E virus
how are viruses infecting the oropharynx principally transmitted?
through saliva

e.g. EBV, CMV, mumps viruses
what is Phthirus pubis?
crabs or pubic lice
what are zoonotic infections?
transmission of microbes from animals to humans, either by:
- direct contact or consumption of animal products
- indirect infection via an invertebrate vector
what are the diseases associated with herpes simplex virus?
primary and recurrent herpes and neonatal herpes in both males and females
what are the diseases associated with hepatitis B virus?
hepatitis in both males and females
what are the diseases associated with human papillomavirus?
cancer of penis in some males

cervical dysplasia and cancer, as well as vulvar cancer in females

condyloma acuminatum in both males and females
what are the diseases associated with HIV?
AIDS in both males and females
what are the important viral STDs?
herpes simplex virus (HSV)
hepatitis B virus (HBV)
human papillomavirus (HPV)
human immunodeficiency virus (HIV)
what are the important bacterial STDs?
Chlamydia trachomatis
Ureaplasma urealyticum
Neisseria gonorrhoeae
Treponema pallidum
Haemophilus ducreyi
Klebsiella granulomatis
what are the diseases associated with chlamydia trachomatis?
urethritis, epididymitis, and proctitis in males

urethral syndrome, cervicitis, bartholinitis, salpingitis and sequelae in females

lymphogranuloma venereum in both males and females
what are the diseases associated with ureaplasma urealyticum?
urethritis in males

nothing in females
what are the diseases associated with neisseria gonorrhoeae?
epididymitis, prostatitis, and urethral stricture in males

cervicitis, endometritis, bartholinitis, salpingitis, and sequelae (infertility, ectopic pregnancy, recurrent salpingitis) in females

urethritis, proctitis, pharyngitis, disseminated gonococcal infection in both males and females
what is proctitis?
an inflammation of the rectum that causes discomfort, bleeding, and occasionally, a discharge of mucus or pus
what are the diseases associated with Treponema pallidum?
syphilis in both males and females
what are the diseases associated with Haemophilus ducreyi?
chancroid in both males and females
what are the diseases associated with Klebsiella granulomatis?
granuloma inguinale (donovanosis) in both males and females
what are the important protozoan STDs?
trichomonas vaginalis
what are the diseases associated with trichomonas vaginalis?
urethritis and balanitis in males

vaginitis in females
what is balanitis?
an inflammation of the foreskin and head of the penis
why is are Shigella species and E. histolytica considered STDs?
typically spread by fecal-oral route, but occasionally spread by oral-anal sex
what is suggested by the presence of an STI in young children?
strongly suggests sexual abuse
what are the initial sites for STIs?
oral pharynx
why are STIs so dependent on person-to-person spread?
the causal organisms are usually short-lived outside the host
what two STIs are commonly associated in the United States?
chlamydia and gonorrhea

infection with both bacteria is so common that the diagnosis of either should lead to treatment for both
what is caused by perinatally acquired Chlamydia trachomatis?
what is a common effect of syphilis on pregnant women?
commonly causes miscarriages
why is diagnosis of STIs in pregnant women so critical?
intrauterine or neonatal STI transmission can often be prevented by treatment of mother or newborn
what is the effect of antiretroviral treatment on incidence of newborn HIV?
decreased from 25% to less than 2%
what STIs can be easily cured with antibiotics?
bacterial infections such as gonorrhea, syphilis, and chlamydia
what are nosocomial infections?
infections acquired in the hospital
by what generic mechanisms do microorganisms cause tissue damage?
- contact or enter host cells and directly cause cell death
- release toxins that kill cells at a distance, release enzymes that degrade tissue components, or damage blood vessels causing ischemic necrosis
- induce host immune responses that cause additional tissue damage
what is tropism?
predilection for viruses to infect certain cells and not others
what factors determine the tropism of a virus?
1) expression of host cell receptors for the virus
2) presence of cellular transcription factors that recognize viral enhancer and promoter sequences
3) anatomic barriers
4) local temperature, pH, and host defenses
what normal cellular receptors are used by HIV to enter cells?
gp120 on HIV binds CD4 and either CXCR4 (on T cells) or CCR5 (on macrophages)
what normal cellular receptors are used by EBV to enter cells?
gp350 on EBV binds CR2 (aka CD21) on B cells
give an example of when a host protease is necessary to enable binding of a virus to host cells?
host protease cleaves and activates influenza virus hemagglutinin
to what cells is the JC virus restricted? why?
JC virus = John Cunningham virus (type of polyomavirus)

oligodendroglia in the CNS, because promoter and enhancer DNA sequences upstream from the viral genes are active in glial cells, but not in neurons or endothelial cells
where do rhinoviruses infect? why?
upper respiratory tract

replicate optimally at the lower temperature of the upper respiratory tract
how does the poliovirus cause direct cytopathic effects?
inactivates cap-binding protein, which is essential for translation of host cell mRNAs but leaves translation of poliovirus mRNAs unaffected
how does the herpes simplex virus cause direct cytopathic effects?
produces proteins that inhibit synthesis of cellular DNA and mRNA and other proteins that degrade host DNA
how does HIV stimulate apoptosis?
causes cell to produce vpr protein, which is a pro-apoptotic protein
what accelerates acute liver failure during hepatitis B infection?
CTL-mediated destruction of infected hepatocytes (the normal immune response to clear the infection)
what are pathogenicity islands?
clusters of virulence genes of bacteria
what determines that the strains of a bacteria are related?
share the same "housekeeping genes"
what are the mobile genetic elements that spread between bacteria and can encode virulence factors?

bacteriophages (viruses that infect bacteria)
what is quorum sensing?
a system of stimulus and response correlated to population density

many bacteria use quorum sensing to coordinately regulate gene expression within a large population

allows unicellular organisms to acquire some of the more complex properties of multicellular organisms (different cells perform different functions)
how does S. aureus use quorum sensing to overcome host defense?
coordinately regulates virulence factors by secreting autoinducer peptides

as population density increases, level of autoinducer peptide increases, stimulating toxin production

within population, some bacteria produce autoinducer peptide while others produce toxins
what is a biofilm?
an aggregate of microorganisms in which cells adhere to each other on a surface

community of organisms living within a viscous layer of extracellular polysaccharides that adhere to host tissues or devices (intravascular catheters and artificial joints)
what is the significance of biofilms?
enhance adherence of bacteria to host tissues

increase virulence of bacteria
- make them inaccessible to immune effector mechanisms
- increase their resistance to antimicrobial drugs

important in persistence and relapse of infections (bacterial endocarditis, artificial joint infections, respiratory infections in ppl with cystic fibrosis)
what are adhesins?
bacterial surface molecules that bind to host cells or extracellular matrix
how does streptococcus pyogenes adhere to host tissues?
protein F and teichoic acid projecting from bacterial cell wall

bind to fibronectin on the surface of host cells and in the ECM
what are pili?
filamentous proteins on the surface of bacteria

stalks are composed of conserved repeating subunits, but tips are composed of variable amino acids
what determines the binding specificity of bacteria?
variable amino acid sequence at the tips of the pili on the surface of bacteria
what pilus is uniquely expressed on strains of E. coli that cause urinary tract infections?
specific P pilus, which binds to a gal(alpha1-4)gal moiety expressed on uroepithelial cells
why are the pili on N. gonorrhoeae bacteria important?
mediate adherence of bacteria to host cells

targets of antibody response against N. gonorrhoeae
what important mechanism allows N. gonorrhoeae to escape the immune system (particularly the humoral arm)?
antigenic variation in the pili expressed on the cell surface
what facultative intracellular bacteria infect epithelial cells?
enteroinvasive E. coli
what facultative intracellular bacteria infect macrophages?
M. tuberculosis
M. leprae
what facultative intracellular bacteria infect epithelial cells and macrophages?
Salmonella typhi
what are the advantages to bacteria of growing inside cells?
allows them to evade certain effector mechanisms of the immune response (antibodies)

facilitates spread of bacteria (e.g. migration of macrophages carrying M. tuberculosis)
how does M. tuberculosis enter macrophages?
activates the alternative complement pathway, resulting in opsonization by C3b

CR3 on macrophages binds C3b, and causes endocytosis of the bacterium
how do gram-negative bacteria enter epithelial cells?
use a complex secretion system consisting of needle-like structures projecting from the bacterial surface that bind to host cells, form pores in the host cell membrane, and then inject proteins that mediate rearrangement of the cell cytoskeleton, facilitating entry
how does Listeria monocytogenes spread from cell to cell?
directly by manipulating the cell cytoskeleton to fuse neighboring cells

allows L. monocytogenes to evade immune effector mechanisms (antibodies)
generically, what do Shigella and E. coli do once inside a host cell?
inhibit host protein synthesis

replicate rapidly

lyse host cell within 6 hours
what does M. tuberculosis do once it's been phagocytosed by macrophages?
blocks fusion of the lysosome with the phagosome

proliferates unchecked within the macrophage
what does L. monocytogenes do once inside host cells?
produces a pore-forming protein (listeriolysin O) and two phospholipases that degrade the phagosome membrane

bacteria can escape phagosome into the cytoplasm
what virulence factors are produced by L. monocytogenes to aid in its escape from host cell phagosomes?
listeriolysin O (pore forming protein)

2 phospholipases (membrane degrading enzymes)
what is a toxin?
any bacterial substance that contributes to illness
what are endotoxins?
components of the bacterial cell that contribute to illness
what are exotoxins?
proteins that are secreted by the bacterium that contribute to illness
what is bacterial endotoxin?
a lipopolysaccharide (LPS) that is a large component of the outer membrane of gram-negative bacteria
what are the components of bacterial endotoxin?
a long-chain fatty acid anchor (lipid A) that is connected to a core sugar chain
- very similar in all gram-negative bacteria

O antigen - variable carbohydrate chain that is attached to the core sugar chain
what is the O antigen?
a variable carbohydrate chain that is attached to the core sugar chain of bacterial endotoxin

used diagnostically to serotype and discriminate between different strains of bacteria
what are the negative side effects of the immune responses triggered by LPS?
septic shock
disseminated intravascular coagulation (DIC)
adult respiratory distress syndrome

mainly occur through induction of excessive TNF, IL-1, IL-12
how is LPS recognized by immune cells?
binds to cell-surface receptor CD14, and this complex then binds to Toll-like receptor 4 (TLR4)

TLR4 is a pattern recognition receptor of the innate immune response and transmits signals that lead to the cellular response
what are the broad categories of exotoxins?

toxins that alter intracellular signaling or regulatory pathways


what is the effect of proteases released by S. aureus?
degrade proteins that hold keratinocytes together, causing epidermis to detach from deeper skin
what are A-B toxins?
toxins produced by bacteria that alter intracellular signalling or regulatory pathways

have an active (A) subunit that has enzymatic activity
have a binding (B) subunit that binds cell surface receptors and delivers the A subunit into the cytoplasm
what are the subunits of A-B toxins?
A subunit = active subunit = subunit with enzymatic activity

B subunit = binding subunit = subunit that binds cell surface receptors and delivers A subunit to cytoplasm
what bacteria produce neurotoxins?
Clostridium botulinum
Clostridium tetani
what do neurotoxins do?
inhibit release of neurotransmitters, resulting in paralysis

A-B toxins, where A subunit interacts specifically with proteins involved in secretion of NTs at the synaptic cleft
how do tetanus and botulism result in death?
respiratory failure due to paralysis of the chest and diaphragm muscles
what are superantigens?
bacterial toxins that stimulate very large numbers of T lymphocytes by binding to conserved portions of the T-cell receptor, leading to massive T-cell proliferation and cytokine release
what causes toxic shock syndrome?
aka TSS

superantigens made by S. aureus and S. pyogenes
what type of hypersensitivity is the inflammatory reaction to M. tuberculosis?
it is a granulomatous inflammatory response caused by a delayed-type (type IV) hypersensitivity reaction
what is the function and cost of the hypersensitivity reaction to M. tuberculosis?
sequesters the bacilli and prevents spread, but also produces tissue damage and fibrosis
what are the pathologic consequences caused by the humoral immune response to S. pyogenes?
following infection with S. pyogenes, the antibodies produced against the streptococcal M protein can cross-react with cardiac proteins and damage the heart OR anti-streptococcal antibodies binding to antigen form immune complexes deposit in glomeruli and cause nephritis
what causes rheumatic heart disease?
antibodies against streptococcal M protein of S. pyogenes cross react with cardiac proteins and damage the heart

seen as a sequelae to S. pyogenes infection
what causes post-streptococcal glomerulonephritis?
antistreptococcal antibodies that bind to streptococcal antigens and form immune complexes deposit in renal glomeruli and produce nephritis

seen as a sequelae to S. pyogenes infection
what are the two major sequelae to S. pyogenes infection?
rheumatic heart disease (streptococcal M antigen antibodies cross reacting with cardiac proteins)

post-streptococcal glomerulonephritis (anti-streptococcal antibody-antigen complexes deposit in glomeruli)
what is an important early event in the development of inflammatory bowel disease?
compromise of the intestinal epithelial barrier, which enables the entry of both pathogenic and commensal microbes and their interactions with local immune cells, resulting in inflammation
what are the evolved means of immune system evasion that have become important determinants of bacterial virulence and pathogenicity?
1) growth in niches that are inaccessible to the immune system
2) antigenic variation
3) resistance to innate immune defenses
4) impairment of effective T-cell antimicrobial responses by specific or nonspecific immunosuppression
what is the advantage for microbes to propagate in the lumen of the intestine or gall bladder?
concealed from cell-mediated immune defenses

C. difficile in intestinal lumen
S. typhi in gallbladder lumen
how do tapeworm larvae evade immune defenses?
form cysts in host tissues that are covered by a dense capsule and are thus inaccessible to host immune cells and antibodies
how do viruses create antigenic variation?
low fidelity of viral RNA polymerases (HIV, influenza virus)

reassortment of viral genome (influenza virus)
how do Trypanosoma species create antigenic variation?
have many genes for their major surface antigen, VSG, and can vary the expression of it
what is the major surface antigen of Trypanosoma species?

have many genes for it and can thereby vary the expression of it to create antigenic variation
what differs between the 80 serotypes of S. pneumoniae?
capsular polysaccharides
what are the cationic antimicrobial peptides? what is their purpose?

provide important initial defense against invading microbes
how is the carbohydrate capsule of pneumonia- or meningitis-causing bacteria an important viulence factor?
shields the bacterial antigens

prevents phagocytosis by neutrophils

(e.g. pneumococcus, meningococcus, H. influenzae)
how does E. coli cause meningitis?
E. coli with the K1 capsule (which contains sialic acid) cannot activate the alternative complement pathway because sialic acid will not bind C3b

these bacteria escape from complement-mediated lysis and opsonization-directed phagocytosis, and subsequently cause meningitis in newborns
what are the effects that toxins produced by bacteria can have on phagocytes?
kill them
prevent their migration
diminish their oxidative burst
how has Salmonella evolved to reduce TLR activation?
modified the lipid moiety of LPS, such that TLR activation is reduced
how does S. aureus inhibit phagocytosis?
covered by protein A molecules that bind to the Fc portion of antibodies, preventing them from opsonizing the bacteria
what bacteria secrete proteases that degrade antibodies?
what bacteria can multiply within phagocytes?
what fungi can multiply within phagocytes?
Cryptococcus neoformans
what protozoans can multiply within phagocytes?
what mechanisms have viruses evolved to combat secreted interferons?
producing soluble homologues of IFN-alpha/beta/gamma receptors that bind to and inhibit actions of secreted IFNs

producing proteins that inhibit intracellular JAK/STAT signaling downstream of IFN receptors

inactivate/inhibit dsRNA-dependent protein kinase (PKR), a key mediator of antiviral effects of IFN
what is PKR?
double-stranded RNA-dependent protein kinase

a key mediator of the antiviral effects of interferon
what is the advantage conferred to viruses by blocking apoptosis in a host cell?
may give the viruses time to complete replication, assembly and exit, promote viral persistence, and contribute to cell transformation
how do herpesviruses evade T cell-mediated immunity?
binds to/alters localization of MHC class I proteins impairing peptide presentation to CD8+ T cells

express MHC class I homologues that act as effective inhibitors of NK cells by engaging killer inhibitory receptors

target MHC class II molecules for degradation, impairing antigen presentation to CD4+ T cells
what viruses have evolved to bind to or alter localization of MHC class I proteins?
DNA viruses (herpesviruses, including HSV, CMV, and EBV)

impairs peptide presentation to CD8+ T cells
what infections are common in individuals with antibody deficiency?
bacterial - S. pneumoniae, H. influenzae, S. aureus

viral - rotavirus, enteroviruses
what infections are common in individuals with T-cell defects?
intracellular pathogens (viruses and some parasites)
what infections are common in individuals with complement protein deficiencies?
S. pneumoniae
H. influenzae
N. meningitidis
what infections are common in individuals with deficiencies in neutrophil function?
S. aureus
gram-negative bacteria
what bacterial respiratory infections are common in patients with cystic fibrosis?
Pseudomonas aeruginosa
Staphylococcus aureus
Burkholdaria cepacia
what infections are common in individuals with sickle cell anemia? why?
infections with encapsulated bacteria such as Streptococcus pneumoniae

these bacteria are normally opsonized and phagocytosed by splenic macrophages, but in sickle cell patients there is a lack of splenic function
what bacterial infection is common in patients with burns?
Pseudomonas aeruginosa
what is the effect of profound neutropenia on pyogenic bacteria?
though they would normally evoke a vigorous leukocyte response, they may cause rapid tissue necrosis with little leukocyte exudation in a profoundly neutropenic host
what is suppurative (purulent) inflammation?
pattern formed by reaction to acute tissue damage, characterized by increased vascular permeability and leukocytic infiltration, predominantly of neutrophils
what attracts neutrophils to the sites of purulent inflammation?
release of chemoattractants from the pyogenic bacteria that evoke the response (extracellular gram-positive cocci and gram-negative rods)
what is the effect of pneumococci on the lungs?
lobar pneumonia that spares the alveolar walls and resolves completely
what is the effect of staphylococci and Klebsiella on the lungs?
destroy alveolar walls and form abscesses that heal with scar formation
diffuse, predominantly mononuclear, interstitial infiltrates that develop acutely are often a response to what?
intracellular bacteria
intracellular parasites

**these are common features of all chronic inflammatory processes**
what type of immune cells are abundant in the primary and secondary lesions of syphilis?
plasma cells
what type of cells predominate in HBV infection or viral infections of the brain?
what is granulomatous inflammation?
a distinctive form of mononuclear inflammation usually evoked by infectious agents that resist eradication and are capable of stimulating strong T cell-mediated immunity (e.g. M. tuberculosis, Histoplasma capsulatum, schistosome eggs)

characterized by accumulation of activated macrophages called "epitheloid cells" which may fuse to form giant cells; sometimes there are central areas of caseous necrosis
what type of organisms usually produce cytopathic-cytoproliferative reactions?
what are the characteristics of cytopathic-cytoproliferative reactions?
cell necrosis or cellular proliferation usually with sparse inflammatory cells
what viruses induce cells to fuse and form polykaryons?
polykaryons = fused, multinucleated cells

measles virus
what is caused by focal cell damage of the skin?
detachment of epithelial cells, forming blisters
what is the appearance of tissue necrosis caused by organisms that secrete powerful toxins?
few inflammatory cells are present

resemble infarcts with disruption or loss of basophilic nuclear staining and preservation of cellular outlines

caused by organisms such as clostridium perfringens that cause such rapid and severe necrosis that tissue damage is the dominant feature
when do clostridia pathogens usually infect?

introduced into muscle tissue by penetrating trauma

infection of the bowel in a neutropenic host
what is caused by Entamoeba histolytica?
colonic ulcers and liver abscesses characterized by extensive tissue destruction with liquefactive necrosis and without a prominent inflammatory infiltrate
what is caused by chronic HBV infection?
cirrhosis of the liver, in which dense fibrous septae surround nodules of regenerating hepatocytes
how many serotypes are there of the mumps virus?
one serotype (therefore infects only once)
how many serotypes are there of the influenza virus?
multiple (can repeatedly infect the same individual because of antigenic variation)
what process can allow the same serotype of a virus to infect the same person repeatedly?
waning of immune response to some transient viruses

(e.g. respiratory syncytial virus)
what is the leading cause of vaccine-preventable death and illness worldwide?
measles (rubeola) virus
what disease is caused by rubeola virus?
measles virus
how many people are affected by measles each year?
more than 20,000,000 people
why are children in developing countries 10-1000 times more likely to die of measles pneumonia than are children in developed countries?
poor nutrition
what caused the incidence of measles infection to decrease dramatically?
licensing of a measles vaccine in 1963
how is diagnosis of measles usually made?
clinical presentation
detection of viral antigen in nasal exudate or urinary sediment
rubeola virus
aka measles virus

ssRNA virus (paramyxovirus family)

only one serotype
what viruses belong to the paramyxovirus family?
measles virus
mumps virus
respiratory syncytial virus
parainfluenza virus
human metapneumovirus
what is the major cause of lower respiratory infections in infants?
respiratory syncytial virus (RSV)
what two cell-surface receptors have been identified for the measles virus?
CD46 (complement regulatory protein that inactivates C3 convertases)

SLAM (molecule involved in T cell activation)
what is CD46?
a complement regulatory protein that inactivates C3 convertases

expressed on all nucleated cells
what is SLAM?
signaling lymphocytic activation molecule

a molecule involved in T-cell activation

expressed on cells of the immune system
what protein on measles virus is bound by CD46 and SLAM?
viral hemagglutinin protein
how is measles virus transmitted?
respiratory droplets
where does measles virus replicate?
initially - upper respiratory epithelial cells

later - local lymphoid tissue

can replicate in epithelial cells, endothelial cells, monocytes, macrophages, dendritic cells, and lymphocytes
what follows replication of the measles virus in lymphatic tissue?
viremia and systemic dissemination of the virus to many tissues (conjunctiva, respiratory tract, urinary tract, small blood vessels, lymphatic system, CNS)
what illnesses can be caused by measles virus?
diarrhea with protein-losing enteropathy
keratitis with scarring and blindness
hemorrhagic rashes (black measles)
what type of immunity controls infection with measles virus?
T cell-mediated immunity controls infection and produces measles

antibody-mediated immunity protects against reinfection
what type of hypersensitivity reaction is the measles rash?
type IV (cell-mediated) hypersensitivity reaction to measles-infected cells in the skin
how does the measles virus result in secondary bacterial and viral infection?
causes transient, but profound, immunosuppression
what is the major cause of measles-related morbidity and mortality?
secondary bacterial and viral infections permitted by the transient, but profound, immunosuppression caused by measles virus
what are the alterations in innate and adaptive immunity caused by measles virus?
defects in dendritic cell and lymphocyte function
what are the rare late complications of measles?
subacute sclerosing panencephalitis

measles inclusion body encephalitis
what is involved in the subacute sclerosing panencephalitis caused by the measles virus?
replication-defective variant of measles may be involved
describe the rash seen with measles infection
blotchy, reddish brown rash

on the face, trunk, and proximal extremities

produced by dilated skin vessels, edema, and a moderate, nonspecific, mononuclear perivascular infiltrate
what are Koplik spots?
ulcerated mucosal lesions in the oral cavity near the opening of Stensen ducts

marked by necrosis, neutrophilic exudate, and neovascularization

seen in patients with measles infection
what are Stensen ducts?
aka parotid gland

the route that saliva takes from the parotid gland into the mouth
what is seen in the lymphoid organs of measles patients?
marked follicular hyperplasia, large germinal centers, and randomly distributed Warthin-Finkeldey cells
what are Warthin-Finkeldey cells?
multinucleate giant cells, which have eosinophilic nuclear and cytoplasmic inclusion bodies

these cells are pathognomic of measles infection

found in the lung, sputum, and lymphoid organs
what is a pathognomic sign?
a particular sign whose presence means that a particular disease is present beyond any doubt (diagnostic disease)
to what viral family does the mumps virus belong?
paramyxovirus family
what are the activities of of the two surface glycoproteins of the mumps virus?
one has hemagglutinin and neuraminidase activities

one has cell fusion and cytolytic activities
how is the mumps virus transmitted?
enters upper respiratory tract via inhalation of respiratory droplets
how does the mumps virus infect individuals?
enters the URT via respiratory droplets

spreads to draining lymph nodes where they replicate in lymphocytes

spread through the blood to the salivary and other glands

infects salivary gland ductal epithelial cells
what cells are infected by mumps virus?
activated T lymphocytes (replication)

salivary gland ductal epithelial cells
in what type of cells does the mumps virus preferentially replicate?
activated T lymphocytes
what happens when mumps virus infects salivary gland ductal epithelial cells?
desquamation of involved cells, edema, inflammation that leads to classic salivary gland pain and swelling of mumps
to what locations does the mumps virus spread after the lymph nodes?
salivary gland ductal epithelial cells

what is the most common extrasalivary gland complication of mumps infection?
Aseptic meningitis

occurs in about 10% of cases
what is aseptic meningitis?
a condition in which the layers lining the brain, meninges, become inflamed and a pyogenic bacterial source is not to blame

many cases of aseptic meningitis represent infection with viruses or mycobacteria that cannot be detected with routine methods
what has reduced the incidence of mumps infection by 99%?
MMR vaccine

live-attenuated mumps virus
what type of vaccine is the MMR vaccine?
vaccine against mumps, measles, and rubella (german measles)

all three viruses in the vaccine are live-attenuated
how is mumps infection diagnosed?
usually by clinical presentation

serology and viral cultures can be used for definitive diagnosis
how often is mumps parotitis bilateral?
70% of cases
how do affected salivary glands appear in mumps parotitis?
cross section - enlarged, doughy consistency, moist, glistening, reddish brown

microscopically - interstitium is edematous and diffusely infiltrated by macrophages, lymphocytes, and plasma cells (compresses acini and ducts)
what happens in mumps orchitis?
marked testicular swelling, caused by edema, mononuclear cell infiltration, and focal hemorrhages

parenchymal swelling may compromise the blood supply and cause areas of infarction (because testis is so tightly contained in tunica albuginea)
what is the result of mumps orchitis?
sterility, caused by scars and atrophy of the testis after resolution of viral infection
what is the result of mumps infection in the pancreas?
destructive lesions that cause parenchymal and fat necrosis and neutrophil-rich inflammation
what is caused by mumps encephalitis?
perivenous demyelination

perivascular mononuclear cuffing
what type of virus is mumps virus?
linear, negative-sense, ssRNA

spherical, enveloped virus
to what genus does poliovirus belong?
what type of virus is poliovirus?
spherical, unencapsulated, positive-sense ssRNA virus
what are the enteroviruses?
(+)ssRNA viruses

- coxsackie viruses
- echoviruses
- poliovirus
- rhinovirus
- enterovirus 70
to what virus family does poliovirus belong?
what diseases are caused by coxsackie viruses?
coxsackievirus A:
- childhood diarrhea and rashes
- viral meningitis

coxsackievirus B:
- myopericarditis
- viral meningitis
what disease is caused by enterovirus 70?
what diseases are caused by echovirus?
viral meningitis
what is the Salk vaccine?
aka Salk formalin-fixed vaccine

killed vaccine that includes all three major strains of poliovirus
what is the Sabin vaccine?
aka Sabin oral vaccine

live-attenuated vaccine that includes all three major strains of poliovirus
what factors have resulted in the virtual elimination of poliovirus?
infects humans but not other animals

only briefly shed

doesn't undergo antigenic variations

effective prevention with Salk (killed) and Sabin (live-attenuated) vaccines
where does poliovirus persist?
parts of Africa
how is poliovirus transmitted?
fecal-oral route
what is the process of infection of poliovirus?
infects tissues of the oropharynx

secreted into saliva and swallowed

multiplies in the intestinal mucosa and lymph nodes (transient viremia and fever)

invades the CNS and replicates in motor neurons of the spinal cord or brain stem
why does poliovirus infect only humans?
uses human CD155 to gain entry into cells but does not bind to cells in other species
what are the outcomes of poliovirus infection?
most are asymptomatic

spinal poliomyelitis (virus replicates in motor neurons of the spinal cord)
bulbar poliomyelitis (virus replicates in motor neurons of the brain stem)
in how many cases of poliovirus infection does the virus invade the CNS?
1/100 cases
what part of the immune system controls poliovirus infection?
antiviral antibodies
how can poliovirus spread to the CNS?
secondary to viremia

retrograde transport along axons of motor neurons
what causes the rare cases of poliomyelitis that occur after vaccination?
mutations of the attenuated viruses to wild-type forms
how is poliovirus infection diagnosed?
viral culture of throat secretions or stool

to what viral family does West Nile virus belong?
what type of virus is West Nile Virus?
spherical, enveloped, (+)ssRNA virus

what is an arbovirus?
aka arthropod-borne virus

virus that is transmitted by a bite from mosquitoes, flies, sand flies, lice, fleas, ticks and mites

most are spherical; all but African swine fever virus have RNA genomes
what is the geographic distribution of West Nile virus?
broad distribution in the old world

outbreaks in Africa, Middle East, Europe, Southeast Asia, and Australia
when was West Nile Virus first detected in the US?
1999 during an outbreak in New York City
what is the major reservoir for West Nile Virus?
wild birds

(develop prolonged viremia, and humans are usually incidental hosts)
aside from mosquitoes, how has West Nile Virus been documented to be transmitted?
blood transfusion
transplanted organs
breast milk
where does West Nile virus replicate after inoculation by a mosquito?
replicates in skin dendritic cells, which migrate to lymph nodes

virus replicates further, enters the bloodstream, and crosses the blood-brain barrier (in some individuals)

infects neurons
what is the importance of CCR5 in West Nile virus infection?
essential host factor to resist neuroinvasive infection
what is the CCR5delta32 allele?
a mutated allele for the chemokine receptor CCR5

contains a 32-base pair deletion in the coding sequence for the CCR5 receptor

in homozygous individuals, it results in a complete loss of function

it is associated with symptomatic and lethal West Nile virus infection, as well as immunity against HIV infection
what are the outcomes of West Nile virus infection?
usually asymptomatic

mild, short-lived febrile illness associated with headache and myalgia (20% of cases)

maculopapular rash in approximately 1/2 of cases
what are the CNS complications of West Nile virus?

not frequent (1/150 clinically apparent infections)
what is the mortality in West Nile infections with meningoencephalitis?
10% mortality

long-term cognitive and neurologic impairment in many survivors
what characteristics have been noted in the brains of patients who died of West Nile virus?
perivascular and leptomeningeal chronic inflammation

microglial nodules


(predominantly involves the temporal lobes and brain stem)
who is at greatest risk for infection with West Nile virus?
immunosuppressed individuals

what are the rare complications of West Nile virus?
how is West Nile virus infection diagnosed?
usually by serology

viral culture and PCR-based tests are also used
what are the four viral families that cause viral hemorrhagic fevers?
what are viral hemorrhagic fevers?
systemic infections, caused by enveloped RNA viruses in four families (arenaviruses, filoviruses, bunyaviruses, flaviviruses)

characterized by fever and bleeding disorders and all can progress to high fever, shock and death in extreme cases
what type of transmission is required for the viruses that cause viral hemorrhagic fevers?
depend on animal or insect host for survival and transmission
what restricts the geographic range of viral hemorrhagic fever viruses?
they are restricted to areas in which their hosts reside
how are humans infected with viral hemorrhagic fever viruses?
come into contact with infected hosts or insect vectors

some (ebola, marburg, lassa) can spread from person to person
what is the spectrum of illnesses caused by viral hemorrhagic fever viruses?
relatively mild acute disease, characterized by fever, headache, myalgia, rash, neutropenia, and thrombocytopenia

severe, life-threatening disease - sudden hemodynamic deterioration, shock
why are viral hemorrhagic fever viruses potential biologic weapons?
infectious properties

morbidity and mortality

absence of therapy and vaccines
what causes the hemorrhagic manifestations in viral hemorrhagic fevers?

severe platelet dysfunction

endothelial dysfunction
what is seen in the liver of a patient with a viral hemorrhagic fever?
necrosis and hemorrhage
where do viruses that cause viral hemorrhagic fever replicate?
endothelial cells

direct cytopathic effects may contribute to disease, but most manifestations are related to activation of innate immune responses
what is caused by viral infection of macrophages and dendritic cells?
release of mediators that modify vascular function and have procoagulant activity
what type of virus are herpesviruses?
large encapsulated viruses with dsDNA genome
what is latency?
inability to recover infectious particles from cells that harbor the virus
what are the three subgroups of herpesviruses?
alpha-group (HSV-1, HSV-2, VZV) - infect epithelial cells; latent infections in neurons

lymphotropic beta-group (CMV, HHV-6, HHV-7) - infect and produce latent infection in a variety of cell types

gamma-group viruses (EBV, HHV-8) - latent infection in lymphoid cells
what disease is caused by HHV-6?
aka human herpesvirus-6

causes exanthem subitum (aka roseola infantum, aka sixth disease)

benign rash of infants
what disease is caused by HHV-7?
aka human herpesvirus-7

doesn't have a known disease association
what are the eight types of herpesviruses?
what is herpesvirus simiae?
Old World monkey virus that resembles HSV-1 and can cause fatal neurologic disease in animal handlers, usually resulting from an animal bite
where do HSV-1 and HSV-2 replicate?
in the skin and mucous membranes at the site of entrance (usually oropharynx or genitals)

spread to sensory neurons that innervate the primary sites of replication
what is caused by HSV-1 and HSV-2 infection of epithelia?
vesicular lesions of the epidermis
how are HSV-1 and HSV-2 spread to sensory neurons?
viral nucleocapsids are transported along axons to the neuronal cell bodies of sensory neurons

establish latent infection in cell body
what nucleic acids remain in the viral nucleus of latent HSV-1 and HSV-2 infections?
viral DNA remains in the nucleus

only latency-associated viral RNA transcripts (LATs) are synthesized
what viral proteins are produced in latent HSV infections?

only latency-associated viral RNA transcripts (LATs) are synthesized

LATs may be miRNAs that confer resistance to apoptosis and thus contribute to virus persistence in sensory neurons
how do HSVs evade antiviral CTLs? how do they evade the humoral immune defenses?
antiviral CTLs - inhibit the MHC class I recognition pathway

humoral - produce receptors for the Fc domain of immunoglobulin; produce inhibitors of complement
what is the major infectious cause of corneal blindness in the United States?

corneal epithelial disease is thought to be due to direct viral damage

corneal stromal disease is immune mediated
what is the major cause of fatal sporadic encephalitis in the United States?

occurs when the virus spreads to the brain, particularly the temporal lobes and orbital gyri of the frontal lobes
what individuals are particularly at risk for disseminated herpesvirus infections?

individuals with compromised cellular immunity
what are Cowdry type A inclusion bodies?
pink to purple, eosinophilic, intranuclear inclusions that consist of intact and disrupted virions with the stained host cell chromatin pushed to the edges of the nucleus

seen in HSV, CMV, and VZV herpesvirus infections
where are the fever blisters (cold sores) found in HSV-infected patients?
facial skin around mucosal orifices (lips, nose)

distribution is frequently bilateral and independent of dermatomes
what causes intraepithelial vesicles (blisters) in HSV-infected patients?
intracellular edema and ballooning degeneration of epidermal cells

they frequently burst and crust over, but some result in superficial ulcerations
what is gingivostomatitis?
vesicular eruption extending from the tongue to the retropharynx, which causes cervical lymphadenopathy

caused by HSV-1 infection, usually seen in children
what is herpetic whitlow?
a lesion (whitlow) on a finger or thumb caused by the herpes simplex virus (HSV-1 or HSV-2)

it is a painful infection that typically affects the fingers or thumbs

occurs in infants (sucking thumb with primary oral HSV-1 infection) and in health care workers (dental and medical; in contact with oral secretions)
what virus causes genital herpes?
more often by HSV-2 than HSV-1 (though, with more oral sex, there is an increase in overlap between the territories of HSV-1 and HSV-2)
how does genital herpes present?
vesicles on the genital mucous membranes as well as on the external genitalia that are rapidly converted into superficial ulcerations, rimmed by inflammatory infiltrate
how is congenital herpes transmitted?
transmitted to neonates during passage through the birth canal of infected mothers
how does congenital herpes (HSV-2) infection present in neonates?
may be mild

more commonly - fulminating with generalized lymphadenopathy, splenomegaly, and necrotic foci throughout the lungs, liver, adrenals, and CNS
where are the necrotic foci in fulminating congenital herpes infections?
what are the two forms of corneal lesions caused by HSV?
herpes epithelial keratitis - typical virus-induced cytolysis of the superficial epithelium

herpes stromal keratitis - infiltrates of mononuclear cells around keratinocytes and endothelial cells (causes neovascularization, scarring, opacification of the cornea, and eventual blindness)
what is kaposi varicelliform eruption?
rare but severe disseminated herpes (HSV-1 or HSV-2) infection that generally occurs at sites of skin damage produced by, for example, atopic dermatitis, burns, or eczema
what is eczema herpeticum?
rare but severe disseminated herpes (HSV-1 or HSV-2) infection that generally occurs at sites of skin damage produced by, for example, atopic dermatitis, burns, or eczema
how does kaposi varicelliform eruption differ from eczema herpeticum?
kaposi - generalized vesiculating involvement of the skin

eczema - confluent, pustular, or hemorrhagic blisters, often with bacterial superinfection and viral dissemination to internal viscera
what is the frequent complication of herpes esophagitis?
superinfection with bacteria or fungi
how is herpes bronchopneumonia introduced?
intubation of a patient with active oral lesions

it is often necrotizing
what can be caused by herpes hepatitis?
liver failure
what two conditions are caused by varicella zoster virus?
aka VZV

chickenpox (acute infection)
shingles (reactivation of latent infection)
when is chickenpox most severe?
it is mild in children, but more severe in adults and in immunocompromised individuals
where does VZV infect?
mucous membranes, skin, neurons

causes a self-limited primary infection in immunocompetent individuals

evades immune responses and establishes a latent infection in sensory ganglia
how is VZV transmitted?
transmitted in epidemic fashion by aerosols

disseminates hematogenously

causes widespread vesicular skin lesions
define hematogenous
involving, spread by, or arising in the blood
what cells does VZV infect?
neurons and/or satellite cells around neurons in the dorsal root ganglia

may recur many years after the primary infection, causing shingles
where is the most frequent and most painful localized recurrence of VZV?
dermatomes innervated by the trigeminal ganglia
how is VZV infection diagnosed?
viral culture

detection of viral antigens in cells scraped from superficial lesions
how long after respiratory infection does a chickenpox rash occur?
approximately 2 weeks
how do the lesions of a chickenpox rash present?
appear in multiple waves centrifugally from the torso to the head and extremities

each lesion progresses rapidly from a macule to a vesicle (resembling a dewdrop on a rose petal)

after a few days, most vesicles rupture, crust over, and heal by regeneration, leaving no scars
how do chickenpox vesicles appear on histologic examination?
contain intranuclear inclusions in epithelial cells
what causes scarring in chickenpox?
bacterial superinfection of vesicles that are ruptured by trauma

leads to destruction of the basal epidermal layer and residual scarring
how does shingles occur?
VZV infects acutely, causing chickenpox

it then lies dormant in the dorsal root ganglia, and after a long latent period, it is reactivated and infects sensory nerves that carry it to one or more dermatomes
how does shingles present?
infects keratinocytes and causes vesicular lesions

associated with intense itching, burning, or sharp pain because of simultaneous radiculoneuritis
when is the pain associated with shingles most severe?
when the trigeminal nerves are involved
what is Ramsay Hunt syndrome (specifically type II)?
disorder that is caused by the reactivation of pre-existing herpes zoster virus in a nerve cell bundle in the head (the geniculate ganglion)

neurons in this ganglion are responsible for the movements of facial muscles, the touch sensation of a part of ear and ear canal, the taste function of the frontal two-thirds of the tongue, and the moisturization of the eyes and the mouth

syndrome specifically refers to the combination of this entity with weakness of the muscles activated by the facial nerve
describe the VZV-infected sensory ganglia that has reactivated VZV in them
dense, predominantly mononuclear infiltrate, with herpetic intranuclear inclusions within neurons and their supporting cells
what disorders are caused by VZV infection?
interstitial pneumonia*
transverse myelitis*
necrotizing visceral lesions*

*= particularly in immunosuppressed individuals
what type of virus is cytomegalovirus?
aka CMV

beta-group herpesvirus

large double-stranded, linear DNA genome, encased within an icosahedral capsid, that is enveloped
to what family does cytomegalovirus belong?
what cells are latently infected by CMV?
monocytes and their bone marrow progenitors
when is CMV reactivation common?
when cellular immunity is depressed
what are the disorders caused by CMV infection?
asymptomatic or mononucleosis-like infection in healthy individuals

devastating systemic infections in neonates and in immunocompromised people
how do CMV-infected cells appear on microscopic examination?
enlarged cell

enlarged nucleus

large nuclear inclusion surrounded by a clear halo (owl's eye)
in what disease does one see "owl's eye" inclusions microscopically?
CMV infection

"owl's eye" inclusions are large nuclear inclusions surrounded by a clear halo
how is CMV transmitted?
transplacental transmission
cervical secretions
vaginal secretions
breast milk
venereal route
respiratory secretions
fecal-oral route
iatrogenic transmission
how is CMV transmitted to neonates?

cervical or vaginal secretions at birth

breast milk after birth
how is CMV transmitted to toddlers during preschool years, especially in day care centers?
what is the dominant mode of CMV transmission after 15 years of age?
venereal spread (sexual transmission)

also spread by respiratory secretions and fecal-oral route
what is the most severe side effect of acute CMV infection?
transient, but severe immunosuppression
what cells are infected by CMV?
dendritic cells

impairs their maturation and ability to stimulate T cells
how do herpesviruses elude immune responses?
downmodulate MHC class I and class II molecules

produce homologues of TNF receptor, IL-10, and MHC class I molecules
what cells are affected by CMV infection in the glandular organs? the brain? the lungs? the kidneys?
glandular organs - parenchymal epithelial cells

brain - neurons

lungs - alveolar macrophages, epithelial cells, endothelial cells

kidneys - tubular epithelial cells, glomerular endothelial cells
what is caused by disseminated CMV?
focal necrosis with minimal inflammation in virtually any organ
what is the result of congenital CMV infection in 95% of cases?
asymptomatic disease
what is cytomegalic inclusion disease?
congenital CMV infection from a mother without protective antibodies

resembles erythroblastosis fetalis
how does cytomegalic inclusion disease present?
- intrauterine growth retardation
- jaundice
- hepatosplenomegaly
- anemia
- thrombocytopenia (and subsequent bleeding)
- encephalitis
- microcephaly
what is microcephaly?
smaller than normal brain
how is diagnosis of neonatal CMV made?
shell-virus culture of urine or oral secretions
what is found in infants who survive congenital CMV infection?
usually permanent deficits, including mental retardation, hearing loss, and other neurologic impairments

not always devastating:
- interstitial pneumonitis
- hepatitis
- hematologic disorder
what is the result of CMV infection acquired by passage through the birth canal or from breast milk?
asymptomatic in vast majority of cases

may develop interstitial pneumonitis, failure to thrive, skin rash, or hepatitis

**acquire maternal antibodies against CMV so the disease is less severe**
what is the most common clinical manifestation of CMV infection in immunocompetent hosts beyond the neonatal period?
infectious mononucleosis-like illness, with fever, atypical lymphocytosis, lymphadenopathy, and hepatomegaly accompanied by abnormal liver function test results, suggesting mild hepatitis

most ppl recover without sequelae, although excretion of the virus may occur in body fluids for months to years
where does CMV remain latent?
what patients are susceptible to severe CMV infection?
immunocompromised individuals (e.g. transplant recipients, HIV-infected individuals)
what is the most common opportunistic viral pathogen in AIDS patients?
cytomegalovirus (CMV)
what organs are affected by serious, life-threatening disseminated CMV infections?
lungs (pneumonitis)
GI tract (colitis)
what happens in pulmonary infection with CMV?
interstitial mononuclear infiltrate with foci of necrosis develops, accompanied by the typical enlarged cells with inclusions

can progress to full-blown acute respiratory distress syndrome
what happens in GI infection with CMV?
intestinal necrosis and ulceration can develop and be extensive, leading to the formation of pseudomembranes and debilitating diarrhea
how is CMV infection diagnosed?
demonstration of characteristic morphologic alterations in tissue sections

viral culture

rising antiviral antibody titer

detection of CMV antigens

PCR-based detection of CMV DNA
what allows viruses like HIV and HBV to escape control by the immune system?
high mutation rate
what is caused by HBV?
aka hepatitis B virus

acute hepatitis
chronic hepatitis
to what viral family does HBV belong?
what type of virus is HBV?

enveloped DNA virus with icosahedral nucleocapsid
what DNA virus uses a reverse transcriptase?
hepatitis B virus (HBV)
how is HBV transmitted?
percutaneously (IV drug use or blood transfusion)


what cells does HBV infect? what causes cellular injury in HBV infection?

cellular injury occurs mainly from the immune response to infected liver cells (not cytopathic effects of the virus)
what is the major determinant of whether a person clears HBV or becomes a chronic carrier?
efficacy of cytotoxic T-lymphocyte response
how is HBV eliminated in a patient?
CTLs destroy infected hepatocytes, which clears the virus as well
how does HBV become an established chronic infection?
the rate of hepatocyte infection outpaces the ability of CTLs to eliminate infected cells

happens in about 5% of adults and 90% of children infected perinatally
what happens to the liver in chronic hepatitis B infection?
develops a chronic hepatitis, with lymphocytic inflammation, apoptotic hepatocytes resulting from CTL-mediated killing, and progressive destruction of liver parenchyma

long term viral replication and recurrent immune-mediated liver injury can lead to cirrhosis and increased risk for hepatocellular carcinoma
how can an individual infected with HBV develop a "carrier state", without progressive liver damage?
hepatocytes are infected but the CTL response is dormant, so there is no cell-mediated damage of liver parenchyma
what viruses have been implicated in the causation of human cancer?
epstein barr virus (EBV)
human papillomavirus (HPV)
hepatitis B virus (HBV)
human t lymphocyte virus (HTLV-1)
what causes infectious mononucleosis?
epstein barr virus (EBV)
what is infectious mononucleosis?
benign, self-limited lymphoproliferative disorder, caused by EBV

characterized by fever, generalized lymphadenopathy, splenomegaly, sore throat, and appearance in blood of mononucleosis cells
with what neoplasms is EBV most notably associated?
B cell lymphomas
nasopharyngeal carcinoma
what are the dangerous outcomes of EBV infection?
when does infectious mononucleosis typically present?
late adolescents or young adults among upper socioeconomic classes in developed nations

childhood in undeveloped nations
how is EBV transmitted?
close human contact, frequently with the saliva during kissing
what is the cellular receptor for EBV?
an EBV envelope glycoprotein binds to CD21 (CR2), the receptor for C3d component of complement, present on B cells
where does EBV infection begin?
nasopharyngeal and oropharyngeal lymphoid tissues, particularly the tonsils
how does EBV gain access to submucosal lymphoid tissue?
transient infection of epithelium
transcytosis into the submucosa
what is the process of EBV infection?
transmitted by saliva during kissing

infection begins in nasopharyngeal and oropharyngeal lymphoid tissues, particularly tonsils

EBV gains access to submucosal lymphoid tissues (via transient epithelial infection or transcytosis)

B cells are infected
what are the two types of B cell infection caused by EBV?
in a minority of cells, there is productive infection with lysis of infected cells and release of virions, which may infect other B cells

in most B cells, there is a latent infection
what is the main reservoir for latent EBV infection?
B cells

patients with X-linked agammaglobulinemia, who do not have B cells, do not develop latent EBV infection
what gene products are produced during latent infection with EBV?
EBNA1 - binds EBV genome to chromosomes, mediating episomal persistence and maintenance

EBNA2 & LMP1 - drive B cell activation and proliferation
what is EBNA1?
gene product of latent EBV infection that binds the EBV genome to chromosomes, mediating episomal persistence and maintenance
what is EBNA2?
gene product of latent EBV infection that works with LMP1 to drive B-cell activation and proliferation

stimulates transcription of many host cell genes, including genes that drive cell cycle entry
what is LMP1?
latent membrane protein 1

works with EBNA2 to drive B-cell activation and proliferation

acts by binding to TNF receptor-associated factors, and activates signaling pathways that mimic B-cell activation by CD40, involved in normal B-cell responses
what happens to activated B cells in EBV infection?
disseminate in the circulation and secrete antibodies with several specificities, including heterophile anti-sheep red blood cell antibodies used for diagnosis of infectious mononucleosis
what are heterophile antibodies?
antibodies that bind to antigens that differ from the antigens that induced them

ex. people with mononucleosis make antibodies that agglutinate sheep or horse red blood cells in the laboratory, but these antibodies do not react with EBV
what is the heterophile antibody test? for what is it specific?
test for heterophile anti-sheep red blood cell antibodies

used for diagnosis of infectious mononucleosis (EBV infection)
when do the symptoms of infectious mononucleosis appear?
upon initiation of the host immune response
what is the most important component of the host immune response to EBV?
cellular immunity mediated by CD8+ cytotoxic T cells and NK cells
what are the atypical lymphocytes seen in the blood that are characteristic of infectious mononucleosis?
EBV-specific CD8+ CTLs
include CD16+ NK cells

large, with abundant cytoplasm containing multiple clear vacuolations, an oval, indented, or folded nucleus, and scattered cytoplasmic azurophilic granules
what accounts for the lymphadenopathy and splenomegaly in infectious mononucleosis?
reactive proliferation of T cells largely centered in lymphoid tissues
what are the antibodies produced in Epstein Barr virus infection?
early in infection - IgM antibodies against viral capsid antigens

later in infection - IgG antibodies that persist for life
what is responsible for acting as the brakes on viral shedding in otherwise healthy individuals?
fully developed humoral and cellular responses to EBV

eliminates B cells expressing the full complement of EBV latency-associated genes
what type of virus is is responsible for Burkitt lymphoma?

chromosomal translocation (most commonly an 8:14 translocation) involving the c-myc oncogene
what is the result of EBV infection on lymph nodes?
enlarged throughout the body, principally in the posterior cervical, axillary, and groin regions

most striking histologic feature is expansion of paracortical areas by activated T cells

follicles (B cell areas) are also hyperplastic but usually mild compared to paracortical areas
what are Reed-Sternberg cells?
malignant cells of Hodgkin lymphoma
in what disease do B cells resemble Reed-Sternberg cells?

**the B cells infected by EBV are the cells that resemble Reed-Sternberg cells**
what is the result of EBV infection on the spleen?
enlarged in most cases

usually soft and fleshy with a hyperemic cut surface

especially vulnerable to rupture (rapid increase in size produces a tense, fragile splenic capsule)

histologic changes = expansion in white pulp follicles and in red pulp sinusoids due to presence of numerous activated T cells
what is the result of EBV infection on the liver?
at most moderate hepatomegaly

histologic features = atypical lymphocytes in portal areas and sinusoids

scattered, isolated cells or foci of parenchymal necrosis may be present

**similar to other forms of viral hepatitis**
what are the atypical presentations of infectious mononucleosis?
malaise, fatigue, and lymphadenopathy

fever with unknown origin without significant lymphadenopathy or other localized findings

hepatitis resembling one of hepatotropic viral syndromes

febrile rash resembling rubella
in increasing order of specificity, on what does the diagnosis of infectious mononucleosis (EBM infection) depend?
1) lymphocytosis with characteristic atypical lymphocytes
2) positive heterophile antibody reaction (monospot test)
3) specific antibodies for EBV antigens (capsid antigens, early antigens or EBV nuclear antigen)
what is a monospot test?
aka heterophile antibody test

test to diagnose infectious mononucleosis (EBV infection)
how long does infectious mononucleosis last?
4-6 weeks

(fatigue may last longer)
what is the most common complication of infectious mononucleosis?
hepatic dysfunction with jaundice, elevated hepatic enzyme levels, disturbed appetite, and rarely even liver failure
what is X-linked lymphoproliferation syndrome?
aka Duncan disease

disorder caused by a defect in SH2D1A gene, which is primarily expressed in CTLs and NK cells

SH2D1A (SAP) participates in a signaling pathway critical for an effective cellular response to EBV-infected B cells

patients are often normal until they are acutely infected with EBV, often during adolescence, when the failure to control EBV infection variously leads to chronic infectious mononucleosis, agammaglobulinemia, and B-cell lymphoma
what type of bacteria are Staphylococcus species?
pyogenic gram-positive cocci that form clusters like bunches of grapes
what bacteria form clusters that look like bunches of grapes?
Staphylococcus sp.
what conditions are caused by infection with Staphylococcus sp.?
skin lesions (boils, carbuncles, impetigo, scalded-skin syndrome)

food poisoning
toxic shock syndrome
what types of infections are commonly caused by Staphylococcus epidermidis?
opportunistic infections in catheterized patients, patients with prosthetic heart valves, and drug addicts
what types of infections are commonly caused by Staphylococcus saprophyticus?
common cause of UTIs in young women
what is clumping factor?
surface receptor on S. aureus that binds to fibrinogen
how does S. aureus build a bridge to bind to host endothelial cells?
expresses surface receptors for fibrinogen, fibronectin, and vitronectin, using these molecules as the bridge
how does S. epidermidis infect prosthetic valves and catheters?
it has a polysaccharide capsule that allows it to attach to the artificial materials and to resist host cell phagocytosis
what is the function of the lipase of S. aureus?
degrades lipids on the skin surface

its expression is correlated with the ability of the bacteria to produce skin abscesses
what is the function of protein A on the surface of Staphylococci?
binds to Fc portion of immunoglobulins, allowing the organism to escape antibody-mediated killing
what is S. aureus alpha toxin?
a membrane-damaging/hemolytic toxin

a pore-forming protein that intercalates into the plasma membrane of host cells and depolarizes them
what is S. aureus beta-toxin?
a membrane damaging (hemolytic) toxin

a sphingomyelinase
what is S. aureus delta toxin?
a membrane damaging (hemolytic) toxin

a detergent-like peptide
what is S. aureus gamma toxin?
a membrane damaging (hemolytic) toxin

lyses erythrocytes
what is leukocidin?
membrane damaging (hemolytic) toxin produced by S. aureus

lyses phagocytic cells
what are the exfoliative A and B toxins produced by S. aureus?
serine proteases that cleave desmoglein 1, which is part of the desmosomes that hold epidermal cells tightly together

cleavage of desmoglein 1 causes keratinocytes to detach from one another and the underlying skin, resulting in a loss of barrier function that often leads to secondary skin infections
where does exfoliation caused by S. aureus occur?
locally at the site of infection (bullous impetigo)

widespread, when secreted toxin causes disseminated loss of superficial epidermis (staphylococcal scalded-skin syndrome)
what is bullous impetigo?
exfoliation, caused by staphylococcal exfoliative A and B toxins, that occurs locally at the site of infection

exfoliation = detachment of keratinocytes from each other and from the underlying skin, causing a loss of barrier function
what is scalded skin syndrome?
widespread exfoliation, caused by staphylococcal exfoliative A and B toxins, that causes disseminated loss of superficial epidermis

exfoliation = detachment of keratinocytes from each other and from the underlying skin, causing a loss of barrier function
what conditions are caused by superantigens produced by S. aureus?
food poisoning

toxic shock syndrome
with what is toxic shock syndrome (TSS) associated with in the public eye?
the use of hyperabsorbent tampons, which became colonized with S. aureus during use

it has become clear though, that TSS can be caused by growth of S. aureus at many sites, most commonly the vagina and infected surgical sites
how does TSS present?
TSS = toxic shock syndrome

renal failure
liver disease
respiratory distress
generalized erythematous rash
soft tissue necrosis at the site of infection
what two bacteria can cause toxic shock syndrome?
Staphylococcus aureus

Streptococcus pyogenes
what conditions are caused by superantigens produced by S. aureus?
food poisoning

toxic shock syndrome
how do superantigens cause problems?
bind to conserved portions of MHC molecules and to relatively conserved portions of T-cell receptor beta chains, which stimulates up to 20% of T lymphocytes

stimulation of T lymphocytes causes release of large amounts of cytokines (TNF and IL-1), which produces a condition similar to septic shock
with what is toxic shock syndrome (TSS) associated with in the public eye?
the use of hyperabsorbent tampons, which became colonized with S. aureus during use

it has become clear though, that TSS can be caused by growth of S. aureus at many sites, most commonly the vagina and infected surgical sites
how does TSS present?
TSS = toxic shock syndrome

renal failure
liver disease
respiratory distress
generalized erythematous rash
soft tissue necrosis at the site of infection
what conditions are caused by superantigens produced by S. aureus?
food poisoning

toxic shock syndrome
what two bacteria can cause toxic shock syndrome?
Staphylococcus aureus

Streptococcus pyogenes
how do superantigens cause problems?
bind to conserved portions of MHC molecules and to relatively conserved portions of T-cell receptor beta chains, which stimulates up to 20% of T lymphocytes

stimulation of T lymphocytes causes release of large amounts of cytokines (TNF and IL-1), which produces a condition similar to septic shock
with what is toxic shock syndrome (TSS) associated with in the public eye?
the use of hyperabsorbent tampons, which became colonized with S. aureus during use

it has become clear though, that TSS can be caused by growth of S. aureus at many sites, most commonly the vagina and infected surgical sites
how does TSS present?
TSS = toxic shock syndrome

renal failure
liver disease
respiratory distress
generalized erythematous rash
soft tissue necrosis at the site of infection
what two bacteria can cause toxic shock syndrome?
Staphylococcus aureus

Streptococcus pyogenes
how do superantigens cause problems?
bind to conserved portions of MHC molecules and to relatively conserved portions of T-cell receptor beta chains, which stimulates up to 20% of T lymphocytes

stimulation of T lymphocytes causes release of large amounts of cytokines (TNF and IL-1), which produces a condition similar to septic shock
around what are staphylococcal skin infections centered?
hair follicles

(excluding impetigo)
what is a furuncle?
aka a boil

a focal suppurative inflammation of the skin and subcutaneous tissue, that begins in a single hair follicle and develops into a growing and deepening abscess that eventually "comes to a head" by thinning and rupturing the overlying skin

occurs either solitary or multiple or recurrent in successive crops

most frequent in moist, hairy areas (face, axillae, groin, legs, and submammary folds)
what is a carbuncle?
deeper suppurative infection than a boil, that spreads laterally beneath the deep subcutaneous fascia and then burrows superficially to erupt in multiple adjacent skin sinuses

typically appear beneath the skin of the upper back and posterior neck (fascial planes favor their spread)
where are furuncles (boils) typically found?
moist, hairy locations

- face
- axillae
- groin
- legs
- submammary folds
where are carbuncles typically found?
beneath the skin of the upper back and posterio neck

the fascial planes in these areas favor the spread of carbuncles
what is hidradenitis?
chronic suppurative infection of apocrine glands, most often in the axilla

caused by S. aureus
what is paronychia?
very painful infection of the nail bed

can be caused by S. aureus
what are felons?
very painful infections of the palmar side of fingertips

can be caused by S. aureus
how do staphylococcal lung infections compare to those caused by pneumococcal lung infections?
similar, but S. aureus lung infections cause much more tissue damage
in what type of patients are S. aureus lung infections typically found?
patients with a hematogenous source, such as an infected thrombus
patients with predisposing conditions, such as influenza
what is Ritter disease?
aka staphylococcal scalded skin syndrome

sunburn-like rash over entire body that evolves into fragile bullae that lead to partial or total skin loss

most frequently occurs in children with staphylococcal infection of the nasopharynx or skin
at what layer of the skin does the desquamation of the epidermis occur in Ritter disease?
aka staphylococcal scalded skin syndrome

granulosa layer
what distinguishes Ritter disease (staphylococcal scalded skin syndrome) from Lyell's disease (toxic epidermal necrolysis)?
Ritter disease - desquamation of epidermis at granulosa layer

Lyell's disease - desquamation of epidermis at epidermal-dermal junction
what is Lyell's disease?
aka toxic epidermal necrolysis

rare, life-threatening dermatological condition that is usually induced by a reaction to medications (drug induced hypersensitivity)

characterized by the detachment of the top layer of skin (the epidermis) from the lower layers of the skin (the dermis) all over the body
to what antibiotics is MRSA resistant?
all available beta-lactam cell-wall synthesis inhibitors

- penicillins
- cephalosporins
why has empiric treatment of staphylococcal infections with beta-lactam antibiotics become less effective?
where previously MRSA was mainly found in healthcare-associated infections, community-acquired MRSA infections are becoming more and more common in many areas
what makes community-acquired strains of MRSA particularly virulent?
these strains of S. aureus commonly produce a potent membrane damaging toxin, which kills leukocytes
what type of bacteria are streptococci?
gram-positive cocci

grow in pairs or chains

produce lactic acid
what post-infectious syndromes are caused by Streptococci?
rheumatic fever (S. pyogenes)
immune complex glomerulonephritis
erythema nodosum
how are beta-hemolytic streptococci typed?
according to their surface carbohydrate (Lancefield) antigens

group A = S. pyogenes
group B = S. agalactiae
what is group A streptococcus? what does it cause?
group A streptococcus = S. pyogenes
- pharyngitis (strep throat)
- scarlet fever
- erysipelas
- impetigo
- rheumatic fever
- toxic shock syndrome
- glomerulonephritis
what is group B streptococcus? what does it cause?
group B streptococcus = S. agalactiae

- colonizes the female genital tract (UTIs)
- causes sepsis in neonates
- causes meningitis in neonates
- causes chorioamnionitis in pregnancy
what is the most important alpha-hemolytic streptococcus?
S. pneumoniae

common cause of community-acquired pneumonia and meningitis in adults
what are the alpha-hemolytic streptococci?
S. pneumoniae
Viridans Group (location preference in parenthesis):
- S. mutans
- S. mitis (cheek region)
- S. sanguinis (no preference of location)
- S. salivarius (dorsal tongue)
what is the viridans group of streptococci?
alpha hemolytic and non-hemolytic streptococci that are normal oral flora; they are also a common cause of endocarditis

(s. mutans, S. mitis, S. sanguinis, S. salivarius)
what is scarlet fever?
a disease caused by exotoxin released by Streptococcus pyogenes
what is erysipelas?
an acute streptococcus bacterial infection of the deep epidermis with lymphatic spread
what is the major cause of dental caries?
Streptococcus mutans
how are Streptococcal infections diagnosed?

rapid antigen test for pharyngitis (strep throat)
what type of bacteria are enterococci?
gram-positive cocci

grow in chains

often resistant to commonly used antibiotics

significant cause of endocarditis and UTIs
what species of streptococci have capsules that resist phagocytosis?
S. pyogenes
S. agalactiae
S. pneumoniae
what are the virulence factors of S. pyogenes?
capsule that resists phagocytosis
M protein (prevents phagocytosis)
C5a peptidase (degrades chemotactic peptide)
phage-encoded exotoxin (causes fever and rash in scarlet fever)
what causes the fever and rash that are common in scarlet fever?
phage-encoded exotoxin produced by S. pyogenes
what causes post-streptococcal rheumatic fever?
anti-streptococcal M protein antibodies and T cells that cross-react with cardiac proteins
why are virulent S. pyogenes referred to as flesh-eating bacteria?
cause a rapidly progressive necrotizing fasciitis
what is pneumolysin?
a cytosolic bacterial protein of Streptococcus pneumoniae that is released on disruption of the bacterial cell

it inserts into host cell membranes and lyses them, greatly increasing tissue damage

it also activates the classical pathway of complement, reducing complement available for opsonization of bacteria
how does S. mutans produce dental caries?
metabolizes sucrose to lactic acid, which causes demineralization of tooth enamel

secretes high-molecular-weight glucans, which promote aggregation of bacteria and plaque formation
what are the virulence factors of enterococci?
antiphagocytic capsule

production of enzymes that cleave host tissues

resistance to antibiotics (including vancomycin)
what is the major contributor to the emergence of enterococci as pathogens?
resistance to antibiotics, including broad-spectrum vancomycin

**other than this, enterococci are considered relatively low virulence bacteria**
what characterizes streptococcal infections?
interstitial neutrophilic infiltrates with minimal destruction of host tissues
what skin lesions are caused by streptococci?
furuncles (boils)

similar to staphylococci, but less likely to cause the formation of discrete abscesses
what is the most common streptococcal infection among middle-aged persons in warm climates?

cutaneous rash on the face or, less frequently, on the body or an extremity caused by exotoxins from superficial infection with S. pyogenes
what are the characteristic features of Erysipelas?
rapidly spreading erythematous cutaneous swelling that may begin on the face or, less frequently, on the body or an extremity

the rash has a sharp, well-demarcated, serpiginous border, and may form a "butterfly" distribution on the face
define serpiginous
slowly progressive or "creeping"

regarding skin ailments in particular, this means that such a disease leaves scar tissue below while continuing to affect the skin above
what is seen on histologic examination of Erysipelas rash?
diffuse, edematous, neutrophilic inflammatory reaction in the dermis and epidermis extending into the subcutaneous tissues

microabscesses may be formed, but tissue necrosis is usually minor
what is the major antecedent of post-streptococcal glomerulonephritis?
streptococcal pharyngitis

aka strep throat
what are the characteristic features of Streptococcal pharyngitis?
epiglottic swelling
punctate abscesses of the tonsillar crypts
sometimes, cervical lymphadenopathy

swelling associated with severe pharyngeal infection may encroach on the airways, especially if there is peritonsillar or retropharyngeal abscess formation
when is Scarlet fever most common?
between ages of 3 and 15 years

associated with pharyngitis caused by S. pyogenes
what are the characteristic features of scarlet fever?
punctate erythematous rash that is most prominent over the trunk and inner aspects of the arms and legs

face is also involved, but usually a small area about the mouth remains relatively unaffected to produce a circumoral pallor

inflammation of the skin usually leads to hyperkeratosis and scaling during defervescence
define defervescence
abatement of a fever as indicated by a decrease in bodily temperature
which types of tonsils are visible in the mouth?
palatine tonsils are visible on examination of the mouth
what are the frequent disease presentations of S. aureus?
what are the frequent disease presentations of S. epidermidis?
what are the frequent disease presentations of S. pyogenes?
pharyngitis (strep throat)
scarlet fever
what are the frequent disease presentations of S. pneumoniae?
lobar pneumonia
what organism is also known as pneumococcus?
Streptococcus pneumoniae
what organism is also known as meningococcus?
Neisseria meningitidis
what organism is also known as gonococcus?
Neisseria gonorrhoea
what are the frequent disease presentations of Neisseria meningitidis?
what are the frequent disease presentations of Neisseria gonorrhoea?
what are the frequent disease presentations of E. coli?
wound infection
what are the important opportunistic bacterial infections?
Escherichia coli
Klebsiella pneumoniae
Enterobacter aerogenes
Proteus mirabilis
Proteus morgagni
Serratia marcescens
Pseudomonas aeruginosa
Clostridium difficile
Mycobacterium tuberculosis
Mycobacterum kansasii
what are the frequent disease presentations of L. pneumophila?
Legionella pneumophila produces Legionnaires disease
what are the frequent disease presentations of B. fragilis?
Bacteroides fragilis produces anaerobic infection
what are the important bacterial infections by pyogenic cocci?
S. aureus
S. epidermidis
S. pyogenes
S. pneumoniae
N. meningitidis
N. gonorrhoea
what are the important gram-negative bacterial infections?
E. coli
Klebsiella pneumoniae
Enterobacter aerogenes
Proteus spp. (mirabilis and morgagni)
Serratia marcescens
Pseudomonas aeruginosa
Bacteroides fragilis
Legionella pneumophila
what are the important contagious childhood bacterial diseases?
Heamophilus influenzae (meningitis, URT & LRT infections)

Bordetella pertussis (whooping cough)

Corynebacterium diphtheriae (diphtheria)
what are the important enteric bacterial infections?
Enteropathogenic E. coli
Shigella spp.
Vibrio cholerae
Campylobacter jejuni
Campylobacter coli
Yersinia enterocolitica
Salmonella spp.
what are the frequent disease presentations of S. typhi?
Salmonella typhi

causes Typhoid fever
what are the frequent disease presentations of C. tetani?
Clostridium tetani

causes tetanus (lockjaw)
what are the frequent disease presentations of C. botulinum?
Clostridium botulinum

causes botulism (paralytic food poisoning)
what are the frequent disease presentations of C. perfringens?
Clostridium perfringens

gas gangrene
necrotizing cellulitis
what are the frequent disease presentations of C. septicum?
Clostridium septicum

gas gangrene
necrotizing cellulitis
what are the frequent disease presentations of C. difficile?
Closridium difficile

Pseudomembranous colitis
(antibiotic-associated diarrhea)
what are the frequent disease presentations of B. anthracis?
Bacillus anthracis

what are the frequent disease presentations of Yersinia pestis?
bubonic plague
what are the frequent disease presentations of Francisella tularensis?
what are the frequent disease presentations of Brucella spp.?
Brucella melitensis
Brucella suis
Brucella abortus

Brucellosis (undulant fever)
what are the frequent disease presentations of Borrelia recurrentis?
Relapsing fever
what are the frequent disease presentations of Borrelia burgdorferi?
Lyme disease
what are the frequent disease presentations of Treponema pallidum?
what are the frequent disease presentations of Nocardia asteroides?
what are the frequent disease presentations of Actinomyces israelii?
what are the important bacterial actinomycetaceae infections?
Nocardia asteroides (Nocardiosis)

Actinomyces israelii (Actinomycosis)
what organism causes Diphtheria?
Corynebacterium diphtheriae

gram-positive rod with clubbed ends
what type of bacteria is Corynebacterium diphtheriae?
slender, gram-positive rod with clubbed ends
how is Corynebacterium diphtheriae transmitted?
aerosolized droplets

skin exudate
what is the only toxin produced by Corynebacterium diphtheriae?
phage-encoded A-B toxin that blocks host cell protein synthesis

A domain catalyzes the covalent transfer of ADP-ribose to elongation factor-2 (EF-2), thereby inhibiting the essential function of EF-2 in translation
how potent is the diphtheria toxin?
a single molecule can kill a cell by ADP-ribosylating, and thus inactivating, more that a million EF-2 molecules
what is the effect of immunization with diphtheria toxoid?
protects immunized individuals from lethal effects of diphtheria toxin

**does NOT prevent colonization with C. diphtheriae**
what kind of vaccine is the diphtheria vaccine?
formalin-fixed toxin vaccine consisting of diphtheria toxoid
where does inhaled C. diphtheriae proliferate?
at the site of attachment on the mucosa of the nasopharynx, oropharynx, larynx, or trachea

forms satellite lesions in the esophagus or lower airways
how does C. diphtheriae cause damage at the site of attachment?
releases exotoxin (diphtheria toxin) which causes necrosis of the epithelium, accompanied by an outpouring of a dense fibrinosuppurative exudate

coagulation of this exudate on the ulcerated necrotic surface creates a tough, dirty gray-black superficial membrane

neutrophil infiltration is intense and accompanied by marked vascular congestion, interstitial edema, and fibrin exudation
what happens when the diphtheria membrane sloughs off its inflamed and vascularized bed?
bleeding and asphyxiation
what happens to the diphtheria membrane when infection is controlled?
it is coughed up or removed by enzymatic digestion, and the inflammatory reaction subsides
other than local effects, what is caused by diphtheria exotoxin?
- generalized hyperplasia of the spleen and lymph nodes
- fatty change in myocardium with isolated myofiber necrosis
- polyneuritis with degeneration of the myelin sheaths and axis cylinders
- fatty change and focal necroses of parenchymal cells in the liver, kidneys, and adrenals
what organism causes Listeriosis?
Listeria monocytogenes

gram-positive, facultative intracellular bacillus
what kind of bacteria is Listeria monocytogenes?
gram-positive rod (bacillus)

facultative intracellular
with what are mini-epidemics of Listeria monocytogenes infections linked?
dairy products*
hot dogs
what populations are particularly at risk for infection with Listeria monocytogenes?
pregnant women
immunosuppressed persons
what is the result of Listeriosis in pregnant women?
aka L. monocytogenes infection

causes amnionitis that may result in abortion, stillbirth, or neonatal sepsis
what is the result of Listeriosis in neonates?
disseminated disease (granulomatosis infantiseptica)

exudative meningitis
what is the result of Listeriosis in immunosuppressed adults?
disseminated disease (granulomatosis infantiseptica)

exudative meningitis
what are internalins?
leucine-rich proteins on the surface of Listeria monocytogenes

bind to E-cadherin on host epithelial cells and induce internalization of the bacterium
what is listeriolysin O?
pore-forming protein produced by Listeria monocytogenes

helps bacterium in escape from the phagolysosome
what proteins are used by Listeria monocytogenes to escape phagolysosomes?
listeriolysin O
two phospholipases
what is ACTA?
bacterial surface protein of Listeria monocytogenes that binds to host cell cytoskeletal proteins and induces actin polymerization

the actin polymerization propels the bacterium into adjacent, uninfected cells
what protein allows Listeria monocytogenes to "hijack" host cell actin cytoskeleton and "rocket" from one cell to the next?

bacterial cell surface protein that binds host cell cytoskeletal proteins and induces actin polymerization, which propels the bacterium into adjacent, uninfected cells
how do resting macrophages internalize L. monocytogenes?
C3 activated on the bacterial surface

(they fail to kill the bacteria)
what is important about the action of macrophages in L. monocytogenes infection?
resting macrophages internalize L. monocytogenes through activated C3 on bacterial surface and fail to kill the bacteria

macrophages activated by IFN-gamma phagocytose and kill the bacteria
what immune response is the major contributor to protection against L. monocytogenes?
IFN-gamma produced by NK cells and T cells
what type of inflammatory pattern is caused by acute infection with Listeria monocytogenes?
exudative pattern of inflammation with numerous neutrophils
what is the difference between the meningitis caused by L. monocytogenes and that caused by other pyogenic bacteria?
they are macroscopically and microscopically indistinguishable
if you find gram-positive, mostly intracellular, bacilli in the CSF, what is the most likely diagnosis?
meningitis caused by Listeria monocytogenes
what is seen in infants born with L. monocytogenes sepsis?
papular red rash over the extremities

listerial abscesses in the placenta

smear of meconium shows gram-positive rods
what lesions are seen in neonates and immunosuppressed adults infected with L. monocytogenes?
focal abscesses alternating with grayish or yellow nodules representing necrotic amorphous basophilic tissue debris

occurs in any organ, including lung, liver, spleen, and lymph nodes
what organism causes anthrax?
Bacillus anthracis

large, spore-forming, gram-positive, rod-shaped bacterium
what type of bacteria is Bacillus anthracis?
large, gram-positive rod

how does B. anthracis make a potent biological weapon?
spores are ground to a fine powder
how is Bacillus anthracis typically transmitted?
exposure to contaminated/infected animals or animal products such as wool or hides
what are the three major anthrax syndromes?
cutaneous anthrax (95% of naturally occuring infections)

inhalational anthrax

gastrointestinal anthrax (uncommon)
what is cutaneous anthrax?
begins as a painless, pruritic papule that develops into a vesicle within 2 days

as the vesicle enlarges, striking edema may form around it, and regional lymphdenopathy develops

after rupture of vesicle, the ulcer becomes covered with a characteristic black eschar, which dries and falls off as the person recovers

caused by Bacillus anthracis
bacteremia is rare
what is inhalational anthrax?
Bacillus anthracis spores are inhaled and the organism is carried by phagocytes to lymph nodes where the spores germinate

release of toxins from germinated B. anthracis causes hemorrhagic mediastinitis

after 1-6 day prodromal illness, there is abrupt onset of increased fever, hypoxis, and sweating

frequent bacteremia and frequent meningitis develop

rapidly leads to shock and death in 1-2 days
what are the characteristics of the prodromal illness caused by inhalation of B. anthracis?
chest/abdominal pain
what is GI anthrax?
caused by eating undercooked meat contaminated with B. anthracis

initially causes nausea, abdominal pain, and vomiting, followed by severe, bloody diarrhea

mortality is over 50%
what are the virulence factors of Bacillus anthracis?
antiphagocytic polyglutamyl capsule

potent exotoxins (A-B toxins; A subunit can be edema factor or lethal factor, B subunit is protective antigen)
what is known as "protective antigen" in relation to B. anthracis? why?
B subunit of anthrax toxin

antibodies against this protein protect animals against the toxin
what is edema factor?
one of two alternate A subunits of anthrax toxin (aka EF)

once in the cytoplasm of cells, EF binds to calcium and calmodulin to form an adenylate cyclase

active EF converts ATP to cAMP, which is an important signaling molecule to stimulate efflux of water from host cell, leading to interstitial edema
what is lethal factor?
one of two alternate A subunits of anthrax toxin (aka LF)

once in the cytoplasm of cells, LF is a protease that destroys mitogen-activated protein kinase kinases (MAPKKs), which regulate the activity of MAPKs, which are important regulators of cell growth & differentiation
what is the process by which anthrax toxin is introduced into cells?
B subunit (protective antigen) binds to a host cell-surface protein

host protease clips of a 20kD fragment

remaining 63kD fragment self-associates to form a heptamer

three A subunits bind (either EF or LF) to the B subunit heptamer

complex is endocytosed

low pH of endosome causes conformational change in B heptamer

B heptamer forms selective channel in endosome membrane

EF and LF move into the cytoplasm through selective channel
what is the typical appearance of anthrax lesions at any site?
necrosis and exudative inflammation with infiltration of neutrophils and macrophages
diagnosis of what is suggested by the presence of large, boxcar-shaped gram-positive extracellular bacteria in chains?
Bacillus anthracis
what is seen in the mediastinum in patients with inhalational anthrax?
numerous foci of hemorrhage

hemorrhagic, enlarged hilar and peribronchial lymph nodes
what is seen on microscopic examination of the lungs in a patient with inhalational anthrax?
perihilar interstitial pneumonia with infiltration of macrophages and neutrophils and pulmonary vasculitis

hemorrhagic lesions associated with vasculitis are present in about half of cases
what is seen in mediastinal lymph nodes in a patient with inhalational anthrax?
macrophages with phagocytosed apoptotic lymphocytes
fibrin-rich edema
where is B. anthracis usually seen if in the lungs?
predominantly in the alveolar capillaries and venules

to a lesser degree, within the alveolar space
where is B. anthracis found in fatal cases of inhalational anthrax?
what type of bacteria are Nocardia spp.?
aerobic, gram-positive rods

catalase positive

stain with acid-fast staining

grow in branched chains (look like mold, but are true bacteria)
what bacteria forms thin aerial filaments resembling hyphae?
Nocardia spp.
where are Nocardia spp. typically found?
in the soil
what populations are particularly at risk for Nocardia infections?
immunocompromised people
what type of infections are caused by Nocardia asteroides?
respiratory infections
what type of infections are caused by Nocardia brasiliensis?
skin infections
what is a common sequelae to respiratory infection with Nocardia asteroides?
meningitis (CNS involvement), presumably after dissemination from the lungs

happens in about 1/5 N. asteroides infections
what is the common thread in most patients with N. asteroides infection?
defects in T cell-mediated immunity, often due to prolonged steroid use, or HIV infection, or diabetes mellitus
how do respiratory infections with N. asteroides typically present?
indolent illness with fever, weight loss, and cough

often mistaken for TB or malignancy
define indolent
causing little or no pain
how do CNS infections with N. asteroides typically present?
indolent illness with varying neurologic deficits depending on the site of infection
how do Nocardia spp. appear in tissue?
slender, gram-positive organisms arranged in branching filaments (chains)

irregular staining gives the filaments a beaded appearacne
what bacteria will stain with acid-fast stains?
Mycobacterium spp.
Nocardia spp.
since Actinomyces appear similar to Nocardia on gram stain of tissue, how can you differentiate them?
Nocardia will stain with acid-fast stains, while Actinomyces will not
what type of inflammatory response is elicited by Nocardia spp.?
at any site of infection, a suppurative response with central liquefaction and surrounding granulation and fibrosis

granulomas do not form
how are gram-negative bacterial infections usually diagnosed?
what type of bacteria are Neisseria spp.?
gram-negative diplococci, flattened on adjoining sides (the pair has the shape of a coffee bean)


what types of sugars can Neisseria spp. use to make lactic acid?
N. gonorrhoeae - glucose only

N. meningitidis - glucose and maltose
on what media do Neisseria spp. grow best?
enriched media such as lysed sheep's blood agar ("chocolate" agar)
what are the two clinically significant species of Neisseria?
N. meningitidis

N. gonorrhoeae
why is N. meningitidis important?
significant cause of bacterial meningitis, particularly among children younger than 2 years of age

common colonizer of oropharynx
how is N. meningitidis transmitted?
respiratory droplets
where is N. meningitidis colonization commonly found?
oropharynx in about 10% of the population at any one time

each episode of colonization lasts, on average, several months

immune response leads to elimination of organism in most people and is protective against subsequent disease with same serotype of bacteria
how many serotypes are there of Neisseria meningitidis?
at least 13
when does invasive disease, caused by N. meningitidis, typically occur?
when people encounter new strains to which they are not immune:
- young children
- young adults in military barracks
- young adults in college dormitories
how does N. meningitidis cause meningitis?
invades respiratory epithelial cells and travels to the basolateral side to enter the blood

the capsule of the bacteria inhibits opsonization and destruction of bacteria by complement

after escaping host response, invades CNS
inherited defects in what part of innate immunity cause severe infections?
defects in complement proteins, C5-C9, which form the membrane attack complex
what is the mortality of N. meningitidis infection?
why is N. gonorrhoeae important?
significant cause of STD, infecting about 700,000 people each year in the US

second most common bacterial causative agent of STDs, behind Chlamydia trachomatis
what are the two most common bacterial causative agents of STDs?
1) Chlamydia trachomatis
2) Neisseria gonorhoeae
what is caused by infection with N. gonorhoeae in men?
what is caused by infection with N. gonorhoeae in women?
asymptomatic infection that may go unnoticed and lead to pelvic inflammatory disease if untreated

PID can cause infertility or ectopic pregnancy
how is infection with N. gonorhoeae diagnosed?
PCR tests

where are local manifestations of N. gonorrhoeae seen?
genital or cervical mucosa, pharynx, or anorectum
in what population of patients are N. gonorrhoeae infections more likely to become disseminated?
those patients lacking complement proteins, C5-C9, that form the membrane attack complex
what is caused by disseminated infection with N. gonorrhoeae in adults and adolescents?
septic arthritis accompanied by a rash of hemorrhagic papules and pustules
what is caused by disseminated infection with N. gonorrhoeae in neonates?
blindness and, rarely, sepsis

eye infection is preventable by instillation of silver nitrate or antibiotics in newborn's eyes, but is still an important cause of blindness in some developing nations
how do Neisseria spp. evade the host immune system?
antigenic variation

(multiple serotypes and special genetic mechanisms which permit a single bacterial clone to change its expressed antigens)
where do Neisseria spp. invade?
nonciliated epithelial cells at the site of entry (nasopharynx, urethra, or cervix)
what two surface proteins of Neisseria spp. undergo antigenic variation?
pili proteins

OPA proteins

**both are involved in binding bacteria to host cells**
how are Neisserial pili proteins altered?
genetic recombination

pili are composed of polypeptides encoded by the pili gene, which consists of a promoter and coding sequences for 10-15 pili protein variants

at any point in time, only one of these coding sequences is juxtaposed to the promoter, allowing it to be expressed

periodically, homologous recombination shuttles one of the other coding sequences next to the promoter, resulting in expression of a different pili variant

if only part of the second coding sequence is swapped, an entirely new chimeric variant is created
what mediates the adherence of N. gonorrhoeae to epithelial cells initially?
long pili, which bind to CD46, a complement regulatory protein expressed on all human nucleated cells
how are Neisserial OPA proteins altered?
N. gonorrhoeae has 3/4 genes for OPA proteins, and N. meningitidis has up to 12

Each OPA gene has several repeats of a 5-nucleotide sequence, which are frequently deleted or duplicated, shifting the reading frame of the gene so that it encodes new sequences, or introducing stop codons

this allows Neisseria spp. to express none, one, or several OPA genes at a time
what are OPA proteins?
named OPA proteins because they make bacterial colonies opaque

proteins located in the outer membrane of Neisseria spp. that increase binding to epithelial cells and promote entry of bacteria into cells
what organism causes Whooping Cough?
Bordetella pertussis

gram-negative coccobacillus
what type of bacteria is Bordetella pertussis?
gram-negative coccobacillus (sphere/rod combination)


oxidase positive
urease negative
nitrase negative
citrate negative


grow in diplococci arrangement
what bacteria are coccobacilli?
Bordetella pertussis
Haemophilus influenzae
Chlamydia trachomatis
what is whooping cough?
acute, highly communicable illness characterized by paroxysms of violent coughing followed by a loud inspiratory "whoop"
what type of vaccine is the pertussis vaccine?
killed bacteria

acellular vaccine (less likely to produce febrile state)
why have rates of pertussis been increasing in the United States, even though effective vaccines are available?
antigenic divergence of clinical strains from vaccine strains

waning immunity in young adults
how is diagnosis of whooping cough made?

culture is less sensitive
where does B. pertussis invade?
colonizes brush border of bronchial epithelium

invades macrophages
what gene locus of B. pertussis coordinates the expression of virulence factors?
Bordetella virulence gene locus (bvg locus)
what is BVGS?
a transmembrane protein in Bordetella pertussis bacteria that "senses" signals that induce expression of virulence factors, and on activation phosphorylates the protein BVGA, which regulates transcription of mRNA for adhesins and toxins
what is BVGA?
protein in Bordetella pertussis bacteria that regulates transcription of mRNA for adhesins and toxins

phosphorylated by BVGS
what is the function of the filamentous hemagglutinin adhesin on the cell surface of B. pertussis?
binds to carbohydrates on the surface of respiratory epithelial cells, as well as to CR3 (Mac-1) integrins on macrophages
how does pertussis toxin paralyze cilia?
pertussis toxin ADP-ribosylates and inactivates guanine nucleotide-binding proteins, so these G proteins no longer transduce signals from host plasma membrane receptors
what is pertussis toxin?
exotoxin produced by Bordetella pertussis that paralyzes the cilia of the respiratory tract

it is composed of five distinct proteins, including catalytic peptide S1, which shares homology with catalytic peptides of cholera toxin and E. coli heat-labile toxin
what is the morphology of Bordetella pertussis infection?
laryngotracheobronchitis that features bronchial mucosal erosion, hyperemia, and copious mucopurulent exudate in severe cases

unless superinfected, alveoli remain open and intact

striking peripheral lymphocytosis

hypercellularity and enlargement of mucosal lymph follicles and peribronchial lymph nodes
what type of bacteria is Pseudomonas aeruginosa?
gram-negative bacillus (rod)

patients with what three conditions are likely to have a fatal infection from Pseudomonas aeruginosa?
cystic fibrosis
severe burns
how does P. aeruginosa cause death in many cystic fibrosis patients?
chronic infection causes pulmonary failure
why are infections with Pseudomonas aeruginosa difficult to treat?
P. aeruginosa is very resistant to antibiotics
where is P. aeruginosa commonly acquired?
hospitals (common nosocomial infection)

has been cultured from washbasins, respirator tubing, nursery cribs, bottles containing antiseptics
what is the link between P. aeruginosa and contact lenses?
Pseudomonas aeruginosa causes corneal keratitis in people who wear contact lenses
what is the link between P. aeruginosa and IV drug abusers?
Pseudomonas aeruginosa causes endocarditis and osteomyelitis in IV drug abusers
in what patients does P. aeruginosa cause external otitis?
external otitis = swimmer's ear

healthy individuals
diabetics (more severe)
how does P. aeruginosa bind to epithelial cells and lung mucin?

adherence proteins
how does P. aeruginosa cause the signs and symptoms of gram-negative sepsis?
expresses an endotoxin
what is alginate?
a mucoid exopolysaccharide produced by Pseudomonas aeruginosa

secreted in the lungs of people with cystic fibrosis to form a slimy biofilm that protects the bacteria from antibodies, complement, phagocytes, and antibiotics
what is the function of exotoxin A expressed by P. aeruginosa?
it inhibits protein synthesis by ADP-ribosylating EF-2, the ribosomal protein

similar to diphtheria toxin
what is the function of exoenzyme S expressed by P. aeruginosa?
ADP-ribosylates RAS and other G proteins that regulate cell growth and metabolism
how does P. aeruginosa lyse red blood cells?
secretes a phospholipase C
how does P. aeruginosa degrade pulmonary surfactant?
secretes a phospholipase C
how does P. aeruginosa degrade IgGs?
secretes an elastase
how does P. aeruginosa degrade extracellular matrix proteins?
secretes an elastase
what causes the vascular lesions that are characteristic of P. aeruginosa infection?
P. aeruginosa produces iron-containing compounds that are extremely toxic to endothelial cells and so cause the vascular lesions
what are the virulence factors of P. aeruginosa?
1) alginate (mucoid exopolysaccharide)
2) exotoxin A (like diphtheria toxin)
3) exoenzyme S (inhibits cell metabolism)
4) secrete phospholipase C
5) secrete elastase
6) iron-containing compounds (toxic to endothelial cells)
what is the morphology of Pseudomonas pneumonia?
necrotizing pneumonia that is distributed through the terminal airways in a fleur-de-lis pattern

striking pale necrotic centers with red, hemorrhagic peripheral areas
what is seen on microscopic examination of pneumonia caused by Pseudomonas?
masses of organisms clouding the tissue with a bluish haze, concentrating in the walls of blood vessels, where host cells undergo coagulative necrosis
what infection is strongly suggested by gram-negative vasculitis accompanied by thrombosis and hemorrhage, when seen in lung?
although not pathognomic, this is highly suggestive of P. aeruginosa pneumonia
what is the frequent result of bronchial obstruction by mucus plugging and subsequent P. aeruginosa infection in cystic fibrosis patients?
bronchiectasis and pulmonary fibrosis

even despite antibiotic treatment and host immune response
what is ecthyma gangrenosum?
an infection of the skin typically caused by Pseudomonas aeruginosa

presents as a round or oval lesion, 1 cm to 15 cm in diameter, with a halo of erythema

a necrotic center is usually present with a surrounding erythematous edge, representing where the organism invaded blood vessels and caused infarctions
what does P. aeruginosa do in skin burns?
proliferates widely, penetrating deeply into the veins and spreading hematogenously

leaves well-demarcated necrotic and hemorrhagic oval skin lesions, called ecthyma gangrenosum

DIC often follows the bacteremia
what organism causes the plague?
Yersinia pestis

gram-negative, facultative intracellular bacterium transmitted from rodents to humans by fleabites or, less often, from human to human by aerosols
what type of bacteria is Yersinia pestis?
gram-negative bacillus (rod)
facultative intracellular
facultative anaerobe
urease negative
lactose fermentation negative
indole negative
what bacteria has a safety-pin appearance on staining?
Yersinia pestis

has bipolar staining properties
what is Black Death?
aka the plague

infection with Yersinia pestis
describe the three great plague pandemics
killed 100 million people in Egypt and Byzantium in the 6th century

killed 25% of Europe's population in 14th & 15th centuries

killed tens of millions of people in India, Myanmar, and China at the beginning of the 20th century
How many cases of plague occur each year worldwide?

wild rodents in rural western US are infected and contribute 10-15 cases per year
what two bacteria are genetically similar to Yersinia pestis? what conditions do they cause?
Yersinia enterocolitica
Yersinia pseudotuberculosis

fecal-oral transmitted ileitis and mesenteric lymphadenitis
where do pathogenic Yersinia proliferate?
within lymphoid tissue
what allows pathogenic Yersinia spp. to kill host phagocytes?
Yop virulon

a complex of genes that encodes proteins that assemble into a type III secretion system, which is a hollow syringe-like structure that projects from the bacterial surface, binds to host cells, and injects bacterial toxins, called Yops (Yersinia outercoat proteins) into the cell
what is the Yop virulon?
complex of genes which enable pathogenic Yersinia spp. to kill host phagocytes

encodes proteins that assemble into a hollow syringe-like structure that projects from the bacterial surface, binds to host cells, and injects bacterial toxins (a type III secretion system) called Yops, or Yersinia outercoat proteins, into the cell
what are the different Yersinia outercoat proteins (Yops) used to neutralize host phagocytes? what is the function of each?
YopE, YopH, YopT - block phagocytosis by inactivating molecules that regulate actin polymerization

YopJ - inhibit signaling pathways that are activated by LPS, blocking inflammatory cytokines
how does Y. pestis ensure its own spread?
forms a biofilm that obstructs the gut of the infected flea, so that the flea must regurgitate before it feeds and thus infects the rodent or human that it is biting
what are the distinctive histologic features of Yersinia pestis?
1) massive proliferation of organisms
2) early appearance of protein-rich and polysaccharide-rich effusions with few inflammatory cells but with marked tissue swelling
3) necrosis of tissues and blood vessels with hemorrhage and thrombosis
4) neutrophilic infiltrates that accumulate adjacent to necrotic areas as healing begins
what are the three presentations of Yersinia pestis infection?
bubonic plague - buboes (lymph node enlargement)

pneumonic plague - pneumonia

septicemic plague - sepsis with striking neutrophilia
where is an infected fleabite typically found in patients with bubonic plague?
on the legs

marked by a small pustule or ulcer
draining lymph nodes enlarge dramatically w/in a few days (become soft, pulpy, and plum colored)
enlarged lymph nodes may infarct or rupture through the skin
how does pneumonic plague present?
severe, confluent, hemorrhagic and necrotizing bronchopneumonia, often with fibrinous pleuritis
how does septicemic plague present?
lymph nodes throughout the body as well as organs rich in mononuclear phagocytes develop foci of necrosis

fulminant bacteremias also induce DIC with widespread hemorrhages and thrombi
what is Chancroid?
aka soft Chancre

acute, sexually transmitted, ulcerative infection caused by Hemophilus ducreyi

one of the most common causes of genital ulcers in Africa and Southeast Asia
where is Chancroid most common?
tropical and subtropical areas among lower socioeconomic groups and men who have regular contact with prostitutes
what is one of the most common causes of genital ulcers in Africa and Southeast Asia?
how prevalent is Chancroid in the United States?

20-50 cases/year for last several years
why is it probable that chancroid is underdiagnosed?
Hemophilus ducreyi must be cultured in special conditions and PCR-based tests are not widely available
what condition is caused by infection with Hemophilus ducreyi?
chancroid (soft chancre)

acute, sexually transmitted, ulcerative infection (causes genital ulcers)
how does chancroid present?
4-7 days after inoculation, the person develops a tender, erythematous papule involving the external genitalia

in males, primary lesion is on penis
in females, primary lesion is in vagina or periurethral area

over several days, the surface of the primary lesion erodes to produce an irregular ulcer (more painful in males than females)
how does the chancroid differ from the primary chancre of syphilis?
the ulcer of chancroid is not indurated, and multiple lesions may be present
what does the base of a chancroid ulcer look like?
covered by shaggy, yellow-gray exudate