Pa Microbiology Test 2

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pathogenicity

Back 1

the ability of a microorganism to cause disease

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virulence

Back 2

the extent of pathogenicity

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contagious or communicable

Back 3

diseases that are spread from an infected animal or person

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endemic

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disease is constantly present in a geographic area

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epidemic

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when the occurrence of the disease exceeds the expected levels

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pandemic

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when an epidemic of a disease become worldwide

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sporadic

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if a disease occurs only occasionally

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incubation period

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the interval between infection and appearance of the first symptoms of the disease; followed by illness and then by convalescence (infectious organism can be spread to others during these stages)

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carriers

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individuals that have acquired sufficient immunity to the disease producing organism to prevent occurrence of symptoms; however, unable to eliminate the agent from the body

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virulence factor: adhesins

Back 10

responsible for adherance;
2 types: bacterial fimbriae and cell surface structures;
are not responsible for disease, their loss rendersw the organism avirulent

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virulence factor: host cell invasion

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organisms able to invade and grow inside host cells where they're protected from host's humoral immune system

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virulence factor: antiphagocytic mechanisms
(4)

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capsules, fimbriae, siderophores, toxins

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capsules

Back 13

most common antiphagocytic mech;
made of polysaccharide, making organism "slippery" to prevent being engulfed
i.e. pneumococci & meningococci

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fimbriae

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bind to a surface component of the phagocyte, preventing close contact necesary for phagocytosis

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siderophores

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vertebrates have evolved different ways of retaining iron so it's available for synthesis of new cell components

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toxins
(10 of them)

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toxic substances excreted from bacterial cell or released after lysis of bacterium;
ie. streptococci, staphylococci

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toxin: hyaluronidase

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breaks down hyaluronic acid, (the intracellular glue that keeps connecgtive tissue together)

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toxin: streptokinase

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activates plasmin (proteolytic enz) and causes dissolution of blood clots allowing spread of streptococci

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toxin: coagulase

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causes coagulation of plasma producing a fibrin clot; prevents phagocytosis-produced by staphylococci

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toxin: collagenase

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causes breakdown of collagen and helps spread the org. - produced by clostridia

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toxin: hemolysins

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induce lysis of host's RBC

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toxin: leukocidins

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kills host's leucocytes

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toxin: enterotoxins

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interact w/GI system to cause diarrhea or dysentery;
2 types: ones that stimulate synthesis of cAMP causing electrolyte imbalance - Vibrio cholera, E coli, B cereus;
ones that inhibit protein synthesis killing intestinal epithelial cells - Shigella, E. coli

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toxin: neutotoxins

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tetanus toxin causes spastic paralysis by blocking inhibitory nerve impulses causing neurons to fire continuously; botulism causes flaccid paralysis preventing Ach release

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toxin: pyrogenic

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produced by group A strept and staph;
termed superAg b/c induce secretion of lg quantities of TNF-a and IL-1 inducing inflammation, shock, death

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toxin: endotoxin

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lipid A part of gram neg cells; results in fever, inflammation, and irreversible shock; binds to macros causing the synthesis of TNF-a & IL-1

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a factor that can restrict microbes to body surfaces

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temperature
ex. rhinovirus restricted to upper resp tract b/c like to replicate @ 33C not, 37C (throat)

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spread of microbes by blood

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if free: they're exposed to body defenses like Ab and phagocytes
if associated: the associated cell can protect them from host defenses and carry them around body

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spread of rabies, HSV, and varicella-zoster virus

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spread by peripheral nerves

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genetic determinants of spread replication

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virulence (determined by adhesion), penetration into cells, anti-phagocytic activity, production of toxins, interaction w/ immune system

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constitution of the host

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the ability of a microorganism to infect and cause disease in a given host
ex. malaria and sickle cell anemia

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2 categories of persistent microbes

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1. those that shed more / less continuously ie. EBV, hep B
2. those that shed intermittently ie. HSV typhoid bacilli, malaria parasites

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4 reasons why viruses good at thwarting immune defenses

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1. invasion is often silent
2. can infect cells for long periods of time without adverse effects (ie. rubella, warts, hep B, EBV)
3. establish intimate molecular relationships with infected cell (like interfering with production of interferons)
4. latency, virus genome continues to be present without producing Ag & only does when virus reactivated

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hit and run infection

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microbe invades, multiplies, and shed within few days, b/f immune defenses have time to react; ie. rhinoviruses, rotaviruses

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Concealment of Ag
(a strategy used by parasites to evade immune sys)

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1. remaining inside cell & not displaying Ag on the surface
2.colonizing privileged sites keeps microbe out of reach of circulating lymphocytes
3. microbes take up host molecules to cover their surface
4. avoid inducing immune response

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types of privileged sites

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skin, intestinal lumen, CNS, joints, testes, placenta, and when virus integrated it's DNA into host cell

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how microbes conceal themselves by taking up host molecules

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Fc receptors are displayed on surface in a useless upside down position - preventing Ab or T cells from attacking it

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Antigenic Variation

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to confuse the host by repeated changes in appearance
ie. African trypanosome
can occur:
1. during course of infection in individual
2. during spread of microbe through host community ie. influenza

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3 types of antigenic variation

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1. mutation
2. recombination
3. gene switching

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antigenic variation: mutation

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ie. influenza virus
mutations in genes coding for hemagglutinin & neuraminidase, causing reduced effectiveness of B & T cell memory;
antigenic drift

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antigenic variation: recombination

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ie. influenza A virus
recombination takes place by exchange of genetic material btw 2 different microbes;
antigenic shift

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antigenic variation: gene switching

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ie. African trypanosome
carries 1000 surface molecules; can switch from one gene to another causing a persistent infection on the host

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immunosuppression

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allows microbe enough time to grow, spread, and shed;
an infection of the immune cells (T, B, macros, dendritic)

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lasting general immunosuppression would be detrimental to microbe b/c.....

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susceptibility to other infections would cause unnecessary damage to host species; (HIV at the limit)

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persistent infections

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represent failure of hos defenses:
1. microbe can persist in the infectious form
2. low infectivity
3. completely non-infectious form, not producing any Ag

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persistent infections important b/c.....

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1. can be reactivated
2. sometimes associated w/chronic disease
3. sometimes associated w/cancers

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Common cold

Back 47

rhinoviruses & coronaviruses cause >50%
most common invader of nasopharynx
transmission: aerosol or by virus-contaminated hands
possess surface molecules that bind them firmly to host cell - not washed away in secretions

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Common cold
Tx

Back 48

anticongestants, analgesics, resolve in 48 hrs

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Pharyngitis & Tonsilitis

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70% caused by viruses
sore throat due to mucosa infected or b/c inflammation in lymphoid tissues

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Mononucleosis

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caused by EBV
tonsils and uvula swollen and covered with white exudate; petechiae present on soft palate

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bacteria responsible for pharyngitis

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Streptococcus pyogenes - commonest & most important to dx
Corynebacterium diphtheriae
Haemophilus influenza

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Complications of S. pyogenes

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1. peritonsillar abscess
2. otitis media, sinusitis
3. scarlet fever
4. rheumatic fever
5. acute glomerulonephritis

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peritonsillar abscess

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uncommon; 1-2 days after recovery of strept, pt develops swelling, redness, protrusion of tonsil that's covered in white exudate; opening mouth is painful; voice muffled; "hot potato speech"; abscess can rupture spontaneously or be drained

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Scarlet fever

Back 54

S. pyogenes produces erythrogenic toxin - causes rash 12-48 hrs after fever; rash has sunburn sandpaper appearance w/goose pimples; "strawberry tongue";
tx: fever dissovles in 12-24 hrs; not tx: septicemia, otits media, pneumonia, rheumatic fever, etc.
occurs in ages 4-8

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Rheumatic fever

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Ab formed to Ag of streptococcal cell wall that react w/sarcolemma of heart; granulomas from in heart about 2-4 wks after sore throat; leads to heart valve disease

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Acute glomerulonephritis

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blood in urine, edema, HTN 1-2 wks after sore throat
tx: penicillin

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bacteria responsible for pharyngitis

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Streptococcus pyogenes (commonest), Corynebacterium diphtheriae, & Haemophilus influenza

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complication of S. pyogenes (5)

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1. peritonsillar abscess
2. otitis media, sinusitis
3. scarlet fever
4. rheumatic fever
5. acute glomerulonephritis

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peritonsillar abscess

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uncommon; 1-2 days after recovery pt develops swelling, redness, white exudate on tonsil; opening mouth is painful; muffled voice; "hot potato speech"

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scarlet fever

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strain of S. pyogenes produces erythrogenic toxin; occurs in ages 4-8; rash appears 12-48 hrs after fever; rash has sunburn sandpaper appearance with goose pimples; if tx, clears in 12-24 hrs, if not, back to normal in 5-7 days; complications septicemia, pneumonia, rheumatic fever, osetomyelitis

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rheumatic fever

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Ab formed to Ag that cross react with sarcolemma of heart; granulomas form in heart 2-4 wks after sore throat; leads to heart valve disease

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acute glomerulonephritis

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immune complexes deposited in glomeruli; blood in urine, edema, HTN 1-2 wks after sore throat

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acute otitis media

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cause: Strep. pneumoniae & H. influenzae; common in infants & small kids b/c eustachian tube open more widely; fever, diarrhea, vomiting; fluid may persist for wks-months

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otitis externa

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infections of outer ear cause irritation and pain;
cause: S.aureus, Candida albicans, Proteus, and Ps. aeruginosa
"swimmers ear"

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acute sinusitis

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facial pain, pus in sinsuses; tx: ampicillin or amoxicillin

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Acute epiglottis

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cause: H. influenza; often in kids; difficulty breathing b/c of respiratory obstruction; extreme care when examining b/c epiglottis can be sucked into airway

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Oral Candidiasis

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prolonged use of broad spectrum of antibiotics allows C. albicans to grow; causes thrush; prevalent when immunity is impaired
Tx: antifungals (nystatin)

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Laryngitis and Tracheitis

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cause: parainfluenza, RSV, influenza; hoarseness, burning pain on breathing in/out; swelling of mucus membrane lead to croup (consists of dry cough and inspiratory stridor - crowing)

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Diphtheria

Back 69

cause: corynebacterium diphtheriae; colonize in larynx, pharynx, nose; form "pseudomembrane" - becomes dark and malodorous, fatal bleeding can occur when removing it or block the airway; toxin can lead to myocarditis & cardia failure; tx: antitoxin, penicillin; prevented by DPT

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Acute lower resp tract infections (6)

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1. whooping cough
2. acute bronchitis
3. acute exacerbations of chronic bronchitis
4. acute bronchiolitis
5. pneumonia
6. measles

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Chronic lower resp tract infections (4)

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1. specific infections of TB & aspergillosis
2. lung abscesses & empyema
3. infections of cystic fibrosis
4. parasite infections

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Whooping cough

Back 72

cause: Bortedella pertussis (gram neg); severe disease of childhood, spread by airborne droplets; organism produces several toxins; incubation period 1-3 wks, then appears like URI followed by 1 wk of non-productive cough that is paroxysmal; complications: CNS, exhaustion, vomiting; prevention: DPT vaccine

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Acute bronchitis

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cause: rhinoviruses, coronaviruses; secondary infections w/ S. pyogenes & H. influenzae; cough most prominent characteristic

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Acute exacerbations of chronic bronchitis

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cough and excessive mucous secretion; other causes: smoking, inhalation of dust or fumes; bacteria not the initial infection but perpetuate the disease: Strep. Pneumoniae, H influenzae
tx: antibiotics

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Bronchiolitis

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cause: mainly RSV, Mycoplasma pneumoniae; restricted to childhood; transmitted by droplets or hands; cough, rapid resp rate, cyanosis, otitis media; infection may spread to lungs

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Lobar pneumonia

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involvement of a specific region of lung; the exudate clots in alveoli and makes them solid;
outcome-respiratory distress

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Bronchopneumonia

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diffuse patchy infection throughout lungs;
outcome: resp distress

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Interstitial pneumonia

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invasion of lung interstitium; characteristic of viral infection;
outcome: resp distress

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Lung abscess

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cavitation and destruction of lung parenchyma;
outcome: resp distress

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most common cause of death of elderly

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pneumonia

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Bacterial pneumonia

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cause: Strep. pneumoniae; tx: penicillin;

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primary atypical pneumonias

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when penicillin was given and pneumonias failed to respond; caused by: M. pneumoniae, Chalmydia psittaci, Legionella pneumophilia, coxiella burnetti

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Bacterial pneumonia dx

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symptoms: chest pain, cough, SOB, difficulty and pain on breathing;
chest radiograph and sputum for diagnosis;
tx: penicillin, ampicillin
prevention: immunization

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viral pneumonia

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1. parainfluenza viruses - cause croup & pneumonia in kids <5
2. adenovirus - only a few cause pneumonia
3. influenza virus - cause endemic, epidemic, pandemic influenza

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Influenza viruses

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3 types - A,B,C
A - causes epidemics and occ pandemics (bird resorvoir)
B - only causes epidemics
C - no epidemics, onlyminor resp illness

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Antigenic drift

Back 86

small mutations constantly occurring in hemagglutinin (H) & neuraminidase (N)

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Antigenic shift

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only occurs w/ Influenza A; a sudden major change in H & N Ag due to recombination btw different 2 strains; can lead to a pandemic

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Influenza:
transmission, symptoms, tx, prevention

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droplet inhalation; chills, malaise, fever, muscle aches, runny nose, cough; usually recover after 1 wk; most common during coldest months; amantidine inhibits A replication if given first 2 days; vaccine

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Measles
symptoms, tx, prevention, complications

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major cause of death in childhood in developing countries; fever, runny nose, conjuctivitis, cough, rash; end result - pneumonia & otitis media; no antiviral tx, Antibiotics given for complciations; vaccine (MMR); encephalitis

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TB
cause, transmission, prevalent with, tx

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Mycobacterium tuberculosis; inhalation in aerosols and dust; prevalent with poverty, malnutrition, poor housing; primarily a disease of the lungs, but may spread;
tx: combo of 3 drugs - isoniazid, rifampicin, ethambutol - given for 6 months

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TB primary infection

Back 91

organisms engulfed by macros, cell mediated response detected 4-6 wks after infection; development of granulomas (tubercles); tubercles may heal spontaneously and persist for a lifetime in healthy individual;

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primary TB

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mild and asymptomatic, 90% doens't proceed further; 10% -develop fatigue, wt loss, weakness, fever, chronic cough ans sputum with blood, death

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allergic bronchopulomonary aspergillosis

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allergic response to Aspergillus Ag; more frequently in pt with asthma

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aspergilloma

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occurrs in patients with preexisting lung cavities or pulmonary disorders

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disseminated disease

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fungus invades lungs of immunocompromised

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Cystic fibrosis

Back 96

most common lethal inherited disease among caucasians; characterized by pancreatic insufficiency, abn sweat electrolyte concentrations, production of very viscid bronchial secretions; Pseudomonas auruginosa colonizes lungs of pt aged 15-20; lung damage occurs by immunologic response to the organism, organism is cause of death

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Lung abscess

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cause: aspiration of respiratory or gastric secretions as result of altered consciousness; ill for 2 wks producing lg amts of foul-smelling sputum;
Tx: anti-anaerobic drug (metronidazole)

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Pleural effusion & empyema

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occurs in 50% pt with pneumonia, infection spreads to pleural space and get purulent exudate (empyema)
Tx: drainage of pus, expansion of lung

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parasitic infections of lower resp tract

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nematodes - migrate through lungs as move to sm intestine:
schistosome larvae - cause mild resp symptoms
Echinococcus granulosus - larvae of tapeworm cause resp distress

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Chlamydia trachomatis (types D-K)

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cause inclusion conjuctivitis; occurs through fingers or in newborn through birth canal - purulent conjuctivitis

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Chlamydia trachomatis (types A-C)

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transmission: contact, flies, fingers, towels;
major cause of blindness worldwide

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trachoma

Back 102

result of chronic repeated infection that leads to scarring of cornea
tx: topical antibiotic tetracycline and doxycycline; prevented by improving hygiene

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3 bacteria that cause conjuctivitis

Back 103

Strep. pneumoniae, H. influnaze, Leptospira

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haemophilus aegyptius

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the common conjuctivitis (pink eye); mild or severe, swelling, of eyelids, photophobia, mucopurulent discharge; Tx: topical application of tetracycline

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conjuctivitis by Nesseria gonorrhea

Back 105

through infected birth canal; prevented by applying erythromycin shortly after birth

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conjuctival infections transmitted by...

Back 106

blood or nervous system

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Toxoplasma gondii

Back 107

can cause chorioretinitis leading to blindness; occurs by swallowing oocycts released by infected cats or by eating meat containing cysts

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parasitic worm infections

Back 108

Echinococcus granulosis (larvae tapeworm) enter the eye forming cysts causing mechanical damage; more common by larvae of nematode Toxocara canis - occurs in dogs; can enter any organ in human causing inflammation