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What's unique to gram-positive organisms?
Teichoic acid in the cell wall -- induces TNF & IL-1
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What's unique to gram-negative organisms?
Endotoxin (encoded within their bacterial DNA); outer cell membrane, thin murein layer, then inner cell membrane
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The 5 gram-positive rods... plus the 2 other gram-positive bacteria (besides Strep & Staph)
- Bacillus, Corynebacterium, Clostridium, Listeria, & TB
- B.C.C.L.
- The other 2 (branching filaments): Actinomyces & Nocardia
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Why can't you Gram-stain each of these? Treponema, Rickettsia, Chlamydia, Legionella, Mycoplasma, Mycobacteria
- Treponema = too thin
- Next 3 = intracellular
- Mycoplasma = no cell wall
- Mycobacteria = high lipid-content cell wall (mycolic acid), even though it is gram-pos
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India ink stain is used for...
Silver stain is used for... (2)
- India = Cryptococcus
- Silver = fungus & Legionella
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To culture N.gonorrhoeae, must grow on this kind of media
Thayer-Martin
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Obligate aerobes
- Nagging Pests Must Breathe.
- Nocardia, Pseudomonas, Mycobacterium TB, Bacillus (so, it needs to form spores to protect itself when no O2)
- That's why TB likes to go to the apices of the lung for reactivation: highest PO2 there. (But, initial infection = gravity takes it down to the lower lobes when you breathe in)
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Obligate anaerobes
Can't Breathe Air: Clostridium, Bacteroides, Actinomyces. Could easily accumulate oxidative damage. (Obviously, that means they're catalase-negative, since catalase would degrade hydrogen peroxide)
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What does vibrio cholerae toxin do?
Increases NaCl pumped out of gut, thanks to inc'd Gs --> adenylyl cyclase --> cAMP
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Corynebacterium diphtheriae toxin
- Inactivates EF-2 (elongation factor-2) --> pharyngitis & pseudomembrane in throat. Could get peripheral neuropathy or cardiomyopathy, too.
- Pseudomonas (Exotoxin A) also inactivates EF-2.
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How does Bordetella pertussis toxin work?
Increases cAMP by inhibiting Gi. Whooping cough.
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How does Clostridium tetani toxin work?
Blocks inhibitory neurotransmitter release (GABA & glycine).
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How does Clostridium botulinium toxin work?
Blocks ACh release. From food that's incompletely cooked, then canned (anaerobic). Floppy baby.
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How does Clostridium perfringens toxin work?
Called lecithinase; breaks down muscle & causes hemolysis. Gas gangrene.
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How C.dif toxin works
Kills enterocytes --> pseudomembranous colitis (red with white exudate). Antibiotics responsible: clindamycin, ampicillin.
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Generalized vs. specialized transduction
- Generalized = bacterial DNA gets trapped inside viral capsid
- Specialized = as viral DNA is excised, flanking bacterial genes may come along with it
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What does catalase do?
Breaks down hydrogen peroxide, which is meant to be antimicrobial (made by PMN's)
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what does coagulase do?
- Enclose the bacterium (Staph) in a fibrin clot.
- (Vs. staphylokinase: lyses clots)
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Rheumatic fever: no "rheum" for SPECCulation
- Subcutaneous nodules, polyarthritis, erythema marginatum rash, chorea, carditis (mitral valve #1)
- All caused by a heart Ag similar to a Group A Strep Ag
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What do enterococci cause?
They're natural GI bacteria. They cause subacute bacterial endocarditis & UTI's. Can't treat w/penicillin G.
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The only bacterium with a protein capsule
Bacillus (D-glutamate), which is a gram-pos rod
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The only gram-pos bacterium with endotoxin
Listeria (mild GI in healthy ppl, meningitis in neonates & immunocomp)
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Actinomyces
Gram-positive, branching filament. Part of normal oral/GI flora, but can cause oral & facial abscesses; pus has yellow sulfur granules.
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Nocardia
Like TB: Gram-pos, acid-fast, pulm infection in immunocompromised
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Ghon focus (& where is it usually found)?
- Walled-off TB (caseous granuloma, calcified). Usually found in lower lobe, since that's where primary infections take place.
- Obv, you're still PPD+ with latent TB... but acid-fast stain is only + if active infection.
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Pott's disease
TB in vertebral body
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Mycobacterium leprae
Leprosy = Hansen's disease. Damages skin & superficial nerves. 2 kinds: Lepromatous leprosy is worse (failed T-cell-mediated immunity); tuberculoid leprosy is self limited.
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Gram-negative, non-lactose-fermenting rods
- P.P.S.S. Proteus, Pseudomonas (oxidase-positive), Shigella, Salmonella.
- But all of these, except Pseudomonas, are still part of the Enterobacter family
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Waterhouse-Friderichsen syndrome
N.mengitides gets into blood --> septic shock, DIC, adrenal insufficiency
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With gonorrhea, who's more likely to be asymptomatic, men or women?
Women (men will have pus & painful urination)
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Enterobacteriaceae
E.coli, Klebsiella, Proteus, Serratia, Salmonella, Shigella. HOKE: H antigen (flagella), O antigen (endotoxin), K antigen (kapsule).
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Salmonella typhi
Fever, rose spots on abdomen, diarrhea. Typhoid Mary = chronic carrier (in gallbladder).
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Bacteroides
Gram-negative, but no endotoxin (the only one... vs. Listeria, the only gram-pos bacterium with endotoxin). When intestine breaks open (trauma, appendicitis, ischemia), bacteria seed the intestine --> abscess.
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Leptospirosis
Gram-neg spirochete that affects the liver: flu-like symptoms, abdominal pain, jaundice. Severe form = Weil's disease: both liver & kidney dysfunction (anemia, hemorrhage, azotemia). Tropics.
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Stages of Lyme disease
- Caused by Borrelia burgdorferi, a Gram-negative spirochete transmitted by the deer tick in summer (mainly).
- 1) Erythema chronicum migrans (chest or butt), flulike sx
- 2) Neuro & cardiac: AV block, Bell's palsy, aseptic meningitis
- 3) Migratory polyarthritis, plus chronic monoarthritis
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