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79 Cards in this Set

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  • Back
What are general characteristics of the Enterobacteriacaea family of bacteria?
G- bacilli
glucose fermentors
oxidase negative
reduce nitrate to nitrites
What are the three antigens used to classify strains of Enterobacteriaceae?
O-antigen - LPS
H-antigen - flagella
K-antigen - capsule
Enterobacteriaceae species can be split into 2 groups: lactose fermentors and lactose non-fermentors. What are the species that occupy these 2 groups?
Lactose fermentors - CEEK

Lactose non-fermentors - ShYPS
What virulence factors are shared by all the Enterobacteriaceae?
Endotoxin (Lipid A of LPS) - causes overproduction of cytokine resulting in endotoxic shock

Capsule - interfere with binding of antibody and action of complement

Antigenic phase variation - altered expression of various H or K antigens

Siderophores - iron-chelating protein to acquire iron, which is essential for bacterial growth

Exotoxins - exported from bacterium and can alter specific cell function leading to disease

Type III secretion systems - directly inject bacterial proteins into host cell cytoplasm, secreted proteins have cytopathic activities
What are the subtypes of E.coli and what diseases do they cause?
UPEC (Uropathogenic E.coli) - cystitis (bladder infections) and pyelonephritis (kidney infections)

MNEC (meningitis associated E.coli) - neonatal meningitis

ETEC (Enterotoxigenic E.coli) - traveler's diarrhea

EPEC (Enteropathogenic E.coli) - childhood diarrhea

EHEC (Enterohemorrhagic E.coli) - bloody diarrhea

EIEC (Enteroinvasive E.coli) - diarrhea similar to invasive Shigella

EAEC (Enteroaggragative E.coli) - persistent diarrhea in children, traveler's diarrhea
What is the mechanism of pathogenicity of UPEC?
UPEC = Uropathogenic E.coli

Adhesins bind to bladder (Type I pili) and kidney (P pili) to initially colonize and protect bacteria from being flushed away during urination

alpha-hemolysin - this exotoxin forms a pore that disrupts the plasma membranes of cells
What is the mechanism of pathogenicity of MNEC?
MNEC = meningitis associated E.coli

75% of isolates have K1 capsular antigen

Adhesins - IbeA and OmpA facilitate adherence and invasion of endothelial cells, facilitating crossing of blood-brain barrier

Serum resistance - OmpA interacts with complement binding protein to protect bacteria from complement mediated killing
What is the mechanism of pathogenicity of ETEC?
ETEC = Enterotoxigenic E.coli

cause of most Traveller's diarrhea

spread through food and water contaminated with human waste

incubation of 24-72 hours

colonize epithelium of small intestine and deliver exotoxins that elicit diarrhea

Heat labile toxin (LT) - plasmid encoded A-B toxin that causes secretory diarrhea by increasing intracellular cAMP levels
Heat stable toxin (ST) - small plasmid encoded peptide that stimulates guanylate cyclase in gut epithelial cells resulting in secretory diarrhea from increased intracellular cGMP

Adhesins - colonization factor antigens (CFA/I, CFA/II, CFA/III) are fimbriae important for adherence to jejunum and ileum epithelial linings
What is the mechanism of pathogenicity of EPEC?
EPEC = Enteropathogenic E.coli

cause of childhood diarrhea in developing countries

bacteria bind to intestinal epithelial cells and disrupt overlying mucous gel, causing fever and bloody diarrhea

colonize epithelium of sm.intestine and subsequently destroy microvilli

Bundle-forming pili (BFP) - responsible for initial attachment to the intestinal epithelium
Type III Secretion (T3SS) - responsible for attachment and effacement lesions, loss of microvilli structure, pedestal formation at point of bacterial attachment, secretes Tir protein that inserts into host cell membrane and acts as a receptor for intimin, enabling tight adherence
What is the mechanism of pathogenicity of EHEC?
EHEC = Enterohemorrhagic E.coli

causes bloody diarrhea, abdominal pain, but no fever or only low-grade fever; in 10% of cases leads to hemolytic-uremic syndrome (HUS)

most frequent serotype is O157:H7

cattle are reservoir - infection acquired from ingesting undercooked meat, unpasteurized milk or juices

Adhesins - Type III Secretion System (T3SS) forms attachment and effacement lesions

Exotoxin - Shiga-like toxin is an A-B subunit toxin that inhibits protein synthesis, often the cause of HUS
How is E.coli diagnosed?
growth on routine media

differentiate from other Enterobacteriaceae by biochemical tests

ETEC cannot be practically diagnosed microbiologically because it is difficult to differentiate from commensal E.coli

EHEC can be differentiated from commensal E.coli because EHEC does not ferment sorbitol
How are E.coli infections treated?
ETEC - rehydration, tetracycline/doxycycline, TMP-SMX, bismuth subsalicylate, ciprofloxacin

EHEC - no antibiotics because they increase incidence of HUS
What are the general characteristics of Salmonella?
G- bacilli with flagella

facultative intracellular pathogen

common cause of diarrhea
causes 15% of food-borne illnesses in US

reservoirs are farm animals, chickens, turtles, other reptiles
What bacteria causes typhoid fever?
Salmonella enterica serovar typhi
What are the mechanisms of pathogenicity of Salmonella enterica?
secrete Salmonella pathogenicity island 1 (SPI-1) type III secretion system in intestines to induce ruffling on surface of enterocytes, leading to bacterial internalization

within enterocytes, bacteria survive and multiply in phagosomes

SPI-2 type III secretion system aids in dissemination of Salmonella to bloodstream
What is the clinical presentation of a patient infected with Salmonella enterica?
diarrhea, nausea, vomiting occur 24-48 hours after ingestion

usually self-limited, lasts 7 days

fever occurs in 50% of cases

Typhoid fever - prolonged fever, persistent bacteremia, constipation or diarrhea
How is Salmonella infection diagnosed?
Growth in agar with routine stool culture
How is Salmonella infection treated?
Diarrhea need not be treated unless immunocompromised patient or severe infection

Typhoid fever and bacteremia treated with antibiotics
What are the general characteristics of Shigella?
G- bacilli

4 important species:

Causes dysentery - cramps, painful straining to pass stood, frequent bloody mucoid stools
What are the medically important species of Yersinia?
Yersinia enterocolitica - causes infectious diarrhea due to consumption of contaminated milk, meat, or water

Yersinia pseudotuberculosis - causes infectious diarrhea, bacteria can spread to mesenteric lymph nodes

Yersinia pestis - cause of the bubonic plague
What are the mechanisms of pathogenicity of Yersinia pestis?
once in bloodstream, bacteria travel to nearest lymph node

bacteria in lymph node leak into bloodstream, where cell lysis releases LPS endotoxin causing septic shock

Adhesins - Ail, chromosomally encoded

T3SS on plasmid confers resistance to phagocytosis via secretion of effector proteins that intoxicate host cell:
YopE - disassembly of actin cytoskeleton
YopH - dephosphorylation of proteins required for phagocytosis
YopJ/P - causes apoptosis of phagocytes

Fra1 - antiphagocytic protein that forms part of a capsule around Y.pestis
What clinical diseases are caused by Yersinia pestis?
Bubonic plague - transmission from rats via flea bites, 2-6 day incubation period, bubo develops near site of flea bite, becomes progressively enlarged, painful, and erythematous, 75% mortality

Pneumonic plague - aerosol spread from person to person, 1-4 day incubation period, sudden onset of chills, fever, headache, myalgias, weakness, productive cough, dyspnea, 90% mortality

Primary septicemic plague - direct inoculation of organism into bloodstream, nausea, vomiting, diarrhea, abdominal pain
How is Yersinia pestis diagnosed?
blood cultures
bubo aspirates and sputum samples
grow on sheep blood agar
Giemsa stain - characteristic bipolar appearance (closed safety pins)
How is Yersinia pestis treated?
What are general characteristics of Klebsiella?
plump G- bacilli
prominent capsule causes mucoid appearance of isolated colonies
2 medically important species:
opportunistic pathogens
cause community-acquired pneumonia, UTI, sepsis, wound infection
What are the mechanisms of pathogenicity of Klebsiella?
Pili for adherence
Polysaccharide capsule prevents complement deposition and phagocytosis
Why is Klebsiella difficult to treat?
often very resistant to antibiotics
What are some general features of Enterobacter, Citrobacter, and Serratia marcescens?
part of Enterobacteriaceae family

cause nosocomial respiratory infections, UTIs, abdominal infections

often resistant to beta-lactam antibiotics, especially cephalosporins
What are general features of Proteus?
common cause of nosocomial and community-acquired UTI

2 important species:

contains urease that splits urea into ammonium hydroxide, causing increase in urine pH and promoting formation of struvite kidney stones

hundreds of flagella per cell cause hypermotility
What are general features of Pseudomonas?
G- bacilli
4 medically relevant species:
What diagnostic test can distinguish Pseudomonas from Enterobacteriaceae?
Catalase test - Pseudomonas is catalase positive and Enterobacteriaceae is catalase negative
What are some general features of P.aeruginosa?
live in moist environments
capable of growing in many different organic compounds
common cause of nosocomial infection
What are the mechanisms of pathogenicity of P.aeruginosa?
pili at end of bacteria function as adhesins

capsule of P.aeruginosa in CF patients convers to mucoidy phenotype, these cells overproduce alginate, an exopolysaccharide that is antiphagocytic

exotoxins - Exotoxin A acts similarly to diphtheria toxin - ADP ribosylates EF-2 and disrupts protein synthesis
LasA and Las B (elastase) are two proteases that act to degrade elastin

T3SS - transfers up to 4 effector proteins (ExoS, ExoT, ExoU, ExoY) into host cells causing disruption of actin cytoskeletons and/or cell lysis

What bacteria colonizes a majority of adult CF patients and what disease does it cause?
What clinical diseases are caused by P.aeruginosa?
Pneumonia in CF patients
nosocomial pneumonia in ventilated patients
bacteremia and sepsis in cancer patients
skin infections in burn patients
catheter associated UTIs
skin lesions called ecthyma gangrenosum
hot tub folliculitis
How can P.aeruginosa be diagnosed?
grows on many types of lab media
produces grape-like odor
produce fluorescent pigments
oxidase positive
How is P.aeruginosa treated?
P.aeruginosa has intrinsic and acquired resistance to multiple antibiotics

aminoglycosides used in conjunction with an agent active against bacterial cell walls (piperacillin, ceftazidime, imipenem, aztreonam)
What are general properties of Legionella?
thin G- bacilli
L.pneumophila is most medically significant species
What are general features of L.pneumophila?
cause of Legionairre's Disease

inhabits natural bodies of water as well as cooling towers where they parasitize amoebae

greater than 10 serogroups exist, but serogroup 1 causes 80% of disease

facultative intracellular pathogen

primarily infects macrophages
What are the mechanisms of pathogenicity of L.pneumophila?
attaches to macrophages and provokes coiling phagocytosis - formation of long thin pseudopod by macrophage that wraps around bacterium and engulfs it in a coiled vesicle

dot genetic locus (defect in organelle trafficking) - necessary for blockage of phagolysosome fusion and ribosome recruitment
What are the clinical diseases caused by Legionella pneumophila?
transmission via aspiration of water or inhalation of aerosol, no human-to-human transmission occurs

nosocomial and community-acquired pneumonia

opportunistic infection - immunocompromised, smokers, alcoholics, and elderly are more susceptible

high fever, respiratory symptoms, headache, change in mental status, nausea, vomiting, diarrhea, hyponatremia (low blood sodium)
How can L.pneumophila be diagnosed?
Dieterle silver staining
poorly stained by Gram staining

grows on buffered charcoal-yeast extract (BCYE) agar, which contains L-cysteine, a required AA

direct fluorescent antibody (DFA) test

Urinary antigen test - detects only L.pneumophila serogroup 1
How is L.pneumophila treated?
high dose of erythromycin - associated with side-effects
What are general characteristics of Vibrio?
G- comma-shaped rod

infections spread via exposure to seawater

3 medically important species:
V.cholerae - causes cholera, a severe form of diarrhea
V.parahaemolyticus - causes gastroenteritis
V.vulnificus - causes gastroenteritis and wound infections in cuts exposed to seawater
What are some general characteristics of Campylobacter jejuni?
curved G- rod

frequent cause of gastroenteritis leading to diarrhea

most common bacterial enteric pathogen in the world
What are general characteristics of Helicobacter pylori?
G- curved rod
grows best under microaerophilic conditions (low oxygen)
possibly the only pathogen of the stomach
What properties of Helicobacter pylori enable it to survive in the stomach?
acid inhibitory protein - blocks production of acid secretion

urease - splits urea into ammonium hydroxide to raise pH, creating an alkaline microenvironment for the organism
What are the mechanisms of pathogenicity of Helicobacter pylori?
acid inhibitory protein blocks acid secretion

urease creates alkaline microenvironment

flagella allows motility through mucous that lines the stomach, facilitating adherence to gastric epithelial cells

exotoxins - VacA, a cytotoxin, causes vacuolation of cultured epithelial cells

Type IV secretion - effector proteins transferred directly to cells, stimulating inflammation
What clinical diseases are associated with Helicobacter pylori?
infection usually asymptomatic

gastric inflammation

peptic ulcer disease

risk factor for adenocarcinoma, non-Hodgkin's lymphona, low-grade B cell mucosa-associated lymphoid tissue (MALT) lymphoma of the stomach
How is H.pylori diagnosed?
histologic examination of tissue biopsy obtained via endoscopy

Giemsa or silver stains

Urease test - biopsy specimens assayed for urease activity

Urea breath tests - pt drinks radio-labeled urea solution, presence of urease causes exhalation of radio-labeled CO2

serological tests for IgG
How are H.pylori infections treated?
2 popular regimens:

Bismuth subsalicylate + tetracycline + metronidazole

Omeprazole (PPI) + clarithromycin + metronidazole
What are general characteristics of Haemophilus?
small G- coccobacilli
facultative anaerobe

2 medically important species:
H.influenzae - causes otis media, sinusitis, bronchitis, epiglottitis, pneumonia, meningitis
H.ducreyi - causes STD similar to syphilis
What are general characteristics of Bordetella?
tiny G- coccobacilli
strict aerobes

3 important species:
B.pertussis - causes whooping cough
B.parapertissus - causes less severe respiratory disease in humans
B.bronchiseptica - causes mild disease in animals
What are the mechanisms of pathogenicity of Bordetella pertussis?
adhesins - pili and filamentous hemagglutinin (FHA) allow adherence to ciliated epithelial cells in upper airway
FHA binds galactose residues on epithelial cells and CR3 on PMNs

bacteria survive inside phagocytes


capsule - only the encapsulated organisms of Bordetella are virulent

Adenylate cyclase toxin - produces cAMP in presence of host cell calmodulin, resulting in inhibition of leukocyte function
Dermonecrotic toxin - may be responsible for localized tissue destruction seen during infection
Tracheal cytotoxin - peptidoglycan fragment that inhibits or kills ciliated cells, pro-inflammatory
Pertussis toxin - A-B subunit toxin, one subunit has enzymatic activity - ADP-ribosylation of host cell G protein, which ultimately causes a rise in cAMP levels
What are the stages of Pertussis disease?
1. Incubation (2 weeks)
2. Catarrhal stage - mild coughing and sneezing, patient very infectious
3. Paroxysmal stage - explosive cough followed by whooping during inhalation, cough may lead to exhaustion, cyanosis, vomiting, and convulsions; resolution is very slow
What are some factors that have lead to an increase in Bordetella pertussis infections?
under-vaccination in infants

under- or misdiagnosis of classic and mild pertussis

incidence of pertussis among older children, adolescents, and adults, who serve as reservoirs for the disease have become an important source of disease transmission to infants and young children who are more susceptible to disease complications
How is Bordetella pertussis diagnosed?
samples for culture collected from nasopharynx and grown on Bordet-Gengou medium or charcoal-containing medium

after 4 weeks, cultures are rarely positive, indicating that symptoms are due to inflammatory response, and not bacteria
How should B.pertussis be treated?
erythromycin is treatment of choice, but should be given before onset of paroxysmal stage because after this stage it is mostly immune response that causes the symptoms
How can B.pertussis infections be prevented?
Whole-cell killed vaccine:
immunity wanes after 2 years
no protection after 12 years
CNS side effects

Acellular vaccines:
fewer side-effects
currently licensed for children
What are some general characteristics of Neisseria?
G- diplococci

2 important species:
N.gonorrhoeae - causes the STD gonorrhea
N.meningitidis - causes meningitis and sepsis
What are general characteristics of Neisseria meningitidis?
5 major serogroups based upon polysaccharide capsule: A,B,C,W-135,Y

types B,C,Y common in the US

most disease in US is sporadic or occurs as part of small epidemics
What are the determinants of pathogenicity of Neisseria meningitidis?
antigenic variation
polysaccharide capsule
iron acquisition
What is the role of pili in the pathogenicity of N.meningitidis?
antigenic variation of the pili can help bacteria avoid host immune response

pilE is the locus on the N.gonorrhoeae chromosome that leads to transcription and translation of pili
at low rates of recombination, silent pil genes reassort with pilE genes, creating DNA recombination to lead to brand new pili genes
What feature of N.meningitidis protects the bacteria from phagocytosis?
antibodies on the polysaccharide capsule
What clinical diseases are associated with Neisseria meningitidis?
Meningococcemia - sudden onset of fever, chills, nausea, vomiting, rash (maculopapular, petechial, or ecchymotic), myalgia, and arthralgias; fulminant meningococcemia patients present with very rapidly progressive illness characterized by shock, disseminated intravascular coagulation (DIC), and multiple organ failure

Meningitis - associated with meningococcemia, but may also occur alone; symptoms include severe headache, confusion, lethargy, vomiting, coma, seizures, focal neurologic signs
How is Neisseria meningitidis diagnosed?
G- diplococci can be seen in samples of CSF

blood or CSF sample culture

counterimmunoelectrophoresis or latex agglutination assays
How is N.meningitidis treated?
Penicillin G

Cephalosporins also very active against N.meningitidis

Chloramphenicol for pts with penicillin allergy
How can N.meningitidis infections be prevented?
vaccine exists for serogroups A,C,W-135,Y

no vaccine exists for serogroup B
What are general characteristics of Bartonella?
G- bacilli that invade endothelial cells and erythrocytes

2 medically important species:

zoonotic infection
What are general characteristics of B.quintana?
transmitted person to person via body louse

causes trench fever and bacillary angiomatosis
What are characteristics of B.henselae?
zoonotic infection - reservoir is household cats

transmitted by cat flea, cat scratch, or cat bite

causes cat-scratch disease - enlargement of lymph nodes following cat scratch or bite
What are general characteristics of Brucella?
small G- coccobacilli
cause disease in humans, cattle, goats, and hogs

infection acquired through contact with mucous membranes, cuts, inhalation, consumption of unpasteurized milk or dairy products

survive inside macrophages due to type IV secretion system
What clinical diseases are associated with Brucella?
nonspecific symptoms - fever, malaise, sweats, nonproductive cough

B.abortis - disease of cattle, infection is mild and self-limiting
B.canis - disease of dogs, foxes, coyotes, infection is mild and self-limiting
B.melitensis - disease of goats and sheep, infections are more serious and tend to be prolonged
B. suis - disease of swine and reindeer, infection can become chronic
How is Brucella diagnosed and treated?
Diagnosis - isolate organism from blood or biopsy specimens, serological tests

Treatment - tetracycline or doxycycline
What are general characteristics of Francisella tularensis?
small G- coccobacillus
facultative anaerobe
infects rabbits, squirrels, muskrats, beavers, and deer

humans infected via contact with infected animal (skin, mucous exposure, ingestion, inhalation, tick bite)

intracellular pathogen

replicates in macrophages by inhibiting phagolysosomal fusion
What are the clinical diseases associated with Francisella tularensis?
Tuleremia - 5 clinical presentations
1. cutaneous ulcer and swollen lymph node at site of tick bite
2. direct eye infection results in conjunctivitis and swollen lymph node
3. sepsis
4. pulmonary infection occurs from inhalation of infected aerosols, high mortality rate
5. GI disease after consumption of infected meat
How can Francisella tularensis be treated and prevented?
Treatment: streptomycin

Prevention: vaccine
What are general characteristics of Pasteurella multocida?
small G- coccobacillus
part of normal mouth and respiratory flora of cats and dogs

human infection from cat or dog bite
What clinical diseases are associated with Pasteurella multocida?
cellulitis after 24hr incubation period

chronic respiratory disease in pts with pulmonary dysfunction

systemic infection in immunocompromised patients