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USMLE I Microbio
By specific organisms and by categories of pathology
77
Microbiology
Graduate
03/05/2013

Additional Microbiology Flashcards

 


 

Cards

Term
How does C. tenani's exotoxin work?
Definition
Cleaves synaptobrevin, blocking vesicle formation & release of GABA & glycine (inhibitory).
Term
How does C. botulinum's exotoxin work?
Definition
Cleaves synaptobrevin, blocking vesicle formation & release of ACh.
Term
What organisms make exotoxin A, shiga toxin, & shiga-like toxin, and how do these work?
Definition
Exotoxin A: P. aeruginosa
Shiga toxin: Shigella
Shiga-like toxin (verotoxin): E. coli
They all bind the 60S ribosome subunit & and inhibit protein synth.
Term
How does C. diphtheriae cause dz?
Definition
It does not invade! It releases an exotoxin (diphtheria toxin) that binds a cell-surface receptor & inhibits protein synthesis.
Term
How does V. cholerae cause diarrhea?
Definition
It does not invade! It causes secretory diarrhea by releasing an exotoxin (cholera toxin) that binds on the gut epithelium & keeps adenylate cyclase active, increasing [cAMP].
Term
How does E. coli cause secretory diarrhea?
Definition
In this case, it does not invade. It releases heat-labile (LT) & heat-stable (ST) exotoxins LT increases [cAMP] & causes crypt cells to secrete more Cl- & villous cells to absorb less Na+. ST increases [cGMP] & causes less cotransport of NaCl into cells. Both result in watery diarrhea.
Term
What are the most common causes of neonatal meningitis?
Definition
S. agalactiae (Group B Strep), E. coli, & Listeria.
Term
What are the most common causes of neonatal pneumonia?
Definition
Group B Strep, E. coli.
Term
How do you distinguish between bacterial, viral, & fungal meningitis?
Definition
Bacterial & fungal will show increased glc & P; bacterial will show PMNs; viral & fungal will show lymphos (but in the former glc & P will be normal).
Term
Top 3 causes of Otitis media & Sinusitis?
Definition
S. penumoniae, HiB, & M. catarrhalis.
Term
Describe 4 key features of Moraxella catarrhalis.
Definition
1.) Gram-
2.) Oxidase+
3.) Diplococci
4.) Aerobic
Term
What is the main cause of Otitis externa?
Definition
P. aeruginosa (GN, oxidase+).
Term
What is the main cause of dental caries?
Definition
Streptococcus mutans (GN, catalase-)
Term
What is the main cause of biliary tract infection?
Definition
E. faecalis (GP, gamma hemolytic, Lancefield Group D strep, hardy growth: in 6.5% NaCl and in bile. Biliary tract infection? Think the one that is hardy and can grow in bile.
Term
Describe the three types of diarrhea caused by protozoa.
Definition
(1) Bloody diarrhea; Entamoeba histolytica
(2) Fatty diarrhea; Giardia lamblia
(3) Watery diarrhea; Cryptosporidium parvum
Term
What is the only protozoan to cause a urogenital infection?
Definition
Trichomonas vaginalis! Lacks a cyst form.
Term
What are the two main agents responsible for rare cases of necrotizing fasciitis?
Definition
S. pyogenes (Group A strep, beta-hemolytic), and C. perfingens (GN rod)
Term
How is the diagnosis of chlamydia made?
Definition
PCR; visualize intracellular inclusions (reticular bodies); iodine stain + (inclusions contain glycogen); Giemsa stain +
Term
What is Fitz-Hugh-Curtis syndrome?
Definition
That's the one when chlamydia, gonorrhea, etc. infects the liver capsule.
Term
What's Reiter's syndrome?
Definition
Chlamydia can spread, esp. in males, to synovial joints & other organs, causing arthritis & conjunctivitis, esp. in HLA-B27 patients.
Term
What are the GP spore-forming bacteria?
Definition
Rods: Clostridium (perfingens [non-motile], botulinum, tetani, difficile [all motile]) & Bacillus (cereus [motile], anthracis [nonmotile])

Beaded/branched filaments: Actinomyces israelii (not acid fast, anaerobe), Nocardia (aerobe, acid fast) (N. asteroides, N. brasiliensis)
Term
Which ABX inhibit cell wall synthesis?
Definition
Penicillins & cephalosporins
Term
What is teichoic acid?
Definition
An important surface antigen in GP bacteria
Term
What occurs in the periplasmic space of which bacteria?
Definition
In the periplasmic space of GN bacteria, beta-lactamases cleave beta-lactams, e.g., penicillin.
Term
What is Toxic Shock Syndrome (TSS)?
Definition
What S. aureus releases TSST-1 and it diffuses systemically, this superantigen promotes excessive cytokine release (e.g., IL-1, TNF)-> acute fever, rash, desquamation on palms & soles, hypotensive shock, possible death.
Term
An ASO+ pharygitis can do what that an ASO+ skin infection can't?
Definition
S. pyogenes can cause a glomerulonephritis either way, but only Rheumatic fever post-pharyngitis.
Term
What are the five most common pediatric diseases with rash?
Definition
Measles (measles virus), Rubella (rubella virus), Scarlet fever (S. pyogenes), Roseola (HHV-6), Erythema infectosum (parvovirus B19)
Term
Evidence of prior infection and 2 of the 5 major Jones criteria are req'd for dx of RF. What are the 5?
Definition
Carditis (endo-, myo-, or peri-), Polyarthritis (sensitization to antigen of joints and heart tissue), Sydenham's chorea, Erythema marginatum rash, & SubQ nodules
Term
Which Strep grow in 40% bile?
Definition
Group D: E. faecalis (grow in 6.5% NaCl) & S. bovis (susceptible to 6.5% NaCl).
Term
Which bacteria of the group Bacillus are motile?
Definition
Bacillus cereus is motile & Bacillus anthracis is nonmotile. Both are spore-forming, aerobic GP rods.
Term
What is the only medically-important bacterium with a protein rather than a polysaccharide capsule?
Definition
Bacillus anthracis
Term
What does Clostridium tetani look like and how does its toxin work?
Definition
It looks like a tennis racket (GP rod w/ a large terminal spore) & its tetanospasmin blocks the release of the inhibitory NTs GABA & glycine from Renshaw interneurons of SC.
Term
How does botulinum toxin work?
Definition
It blocks ACh release at CNs (diplopia, dysarthria, dysphagia), NMJ (symmetric descending paralysis from head to extremities), & postganglionic parasymp nerve endings/peripheral ganglia (dizziness, dry throat, ptosis)
Term
Why shouldn't infants consume honey?
Definition
Because it might contain Clostridium botulinum spores.
Term
How does pseudomembranous colitis typically evolve?
Definition
Tx w/ amoxicillin/clindamycin --> C. difficile survives by forming spores --> Germinate in an environment with plenty of room --> release toxin A (alters fluid secretion-->watery diarrhea); release toxin B (cytotoxic to epithelial cells-->pseudomembranes. Toxin B present in feces.
Term
What three pathologies can C. perfringens cause, and what makes it special?
Definition
It is the only non-motile Clostrium family member. It can cause (1) cellulitis, (2) gas gangrene, & (3) food poisoning (enterotoxin inhibits glc transport & damages epithelium)-- diarrhea but no fever/vomiting!
Term
What are the exceptions to the GP/GN endotoxin thing?
Definition
Listeria monocytogenes is the only GP WITH an endotoxin & Bacteroides are the only GN WITHOUT.
Term
I have tumbling motility, I can survive intracellularly AND extracellularly, & I am catalase+. Who am I?
Definition
Listeria monocytogenes, & I can cause listeriosis (meningitis & sepsis in immunocompromised neonates). I also survive in poorly-pasteurized/unpasteurized milk.
Term
I have a "Chinese letters" appearance on potassium tellurite culture. Who am I?
Definition
Corynebacterium diphtheriae. Don't try to scrape away my pseudomembranes (b/c bleeding & toxin spread might result). I can cause myocarditis, arrhythmia, & polyneuritis.
Term
I form beaded filaments within yellow sulfur granules. Who am I?
Definition
Actinomyces israelii. I am part of the normal oral cavity, GI, and female GU flora. I like to form abscesses that spread into ANY contiguous tissue, forming sinus tracts.
Term
What is an oddball cause of a caseating granuloma?
Definition
Nocardia asteroides/brasiliensis! Can cause abscesses in kidney & brain in the immunocompromised, & can cause a local foot infection called mycetoma.
Term
How does the lab tell the three GN diplococci apart?
Definition
Neisseria meningitidis is a maltose AND glucose oxidizer; Neisseria gonorrhoeae is a glucose oxidizer; Morexella catarrhalis is oxidase+.
Term
Which bug requires factors V & X to grow?
Definition
H. influenzae
Term
What is Waterhouse-Friderichsen syndrome?
Definition
When N. meningitidis invades systemically, causing necrosis of the adrenals and subsequent adrenal insufficiency.
Term
What is the most common cause of septic arthritis in sexually active individuals?
Definition
N. gonorrhea (grows on Thayer-Martin media)! Antigenic variation stymies vaccines & allows for recurrent infection.
Term
How do EHEC & EIEC cause illness?
Definition
Shiga-like toxins 1 & 2 inactivate 60s ribosomal subunit --> blocked protein synthesis.
Term
Where do Salmonella typhi (encapsulated) live in an individual who is a carrier?
Definition
In the gallbladder, often in gallstones, waiting to to reenter bowel lumen and spread via stool.
Term
What produces struvite kidney stones?
Definition
Proteus mirabilis elaborates urease, which creates alkaline urine, a favorable environment for the precipitation of struvite.
Term
Who does "rice water" diarrhea?
Definition
Vibrio cholerae (oral rehydration with Na+glucose, to capitalize on cotransporters in the SI).
Term
How P. aeruginosa (blue-green colonies, fruitdy odor) & C. diphtheriae's toxins work?
Definition
Ribosylation of host EF2-->inhibition of protein synthesis.
Term
What is the second most common cause of bacterial pneumonia in pts w/ COPD?
Definition
Moraxella catarrhalis (GN diplococci, oxidase+, tributyrin hydrolyzer), behind H. influenzae.
Term
A 2-yr-old girl returns to her pediatrician one week after being started on amoxicillin for an ear infection. She has new-onset yellow discharge from her right ear. What is the bug?
Definition
M. catarrhalis, normal colonizer of nasopharynx. About 95% produce beta-lactamase, so tx is amoxicillin+clavulanate.
Term
Many cases of Guillain-Barre Syndrome are thought to be complications of infection by which bug?
Definition
Campylobacter jejuni (curved GN bacillus, urease-, grows well at 42C)
Term
What are the three most common causes of diarrhea in the world?
Definition
C. jejuni, rotavirus, & ETEC.
Term
What common GI flora member makes Vit K for the host?
Definition
B. fragilis (only GN w/o typical LPS=no ability to cause DIC/shock!)
Term
What bug poses an especially big risk to asplenic patients?
Definition
Hib, b/c encapsulated organisms are typically primarily destroyed in the spleen after opsonization. "Non-typable" H. influenzae (unencapsulated) most commonly cuases pneumonia in COPD pts.
Term
What are the four main causes of atypical pneumonia?
Definition
Mycoplasma, Legionella, Chlamydia, & viruses.
Term
How does pertussis toxin work?
Definition
It is an AB toxin that ADP-ribosylates & inactivates Gi protein-->uninhibited adenylate cyclase activity-->increased cAMP-->lymphocytosis & decreased phagocytosis.
Term
What can you get from unpasteurized goat cheese that will give you an undulating fever?
Definition
Brucellosis (Brucella spp, GN pleomorphic coccobacillus, anaerobic, facultative intracellular).
Term
If you are raising rabbits in Arkansas, Oklahoma, or Missouri, what might you get infected with?
Definition
Francisella tularensis (GN, pleomorphic coccobacilli, req's cysteine for growth) most commonly causes tularemia: an ulcer with a black base & LAD. The only 2 live-attenuated vaccines for bacteria are BCG & F. tularensis.
Term
What can cause either cellulitis or osteomyelitis following a cat or dog bite?
Definition
Pasteurella multocida (GN pleomorphic coccobacilli, bi-polar staining, oxidase+, catalase+).
Term
What causes cat scratch disease?
Definition
Bartonela henselae (GN, pleomorphic coccobacilli), which can cause a variety of symptoms, incl. regional LAD, fever, ocular involvement, HSM, & bacillary angiomatosis (granulomatous infl.).
Term
What TB's means for evading phagocytosis?
Definition
Sulfatides in cell wall inhibit phagosome from fusing to lysosome.
Term
What does the Quantiferon Gold assay actually measure?
Definition
It measures IFN-gamma released by lymphocytes exposed to M. tb antigens.
Term
What is an easy way to remember TB treatment?
Definition
RIPES: Rifampin, INH, Pyrazinamide, Ethambutol, & Streptomycin. If the individual is PPD+, tx w/ INH.
Term
What is a classical clinical finding of tuberculoid leprosy?
Definition
Palpable thickened nerves (e.g., posterior tibial, ulnar). Remember than M. leprae likes to grow at cooler sites of the body (e.g., face, extremities).
Term
What are the placenta-crossing ToRCHES organisms?
Definition
TOxoplasma gondii, Rubella, CMV, HIV, hErpes, & Syphilis.
Term
What are three ways to diagnose syphilis?
Definition
(1) Dark-field microscopy (spirochetes not visible on Gram stain); (2) VDRL (nonspecific) detects reagin antibodies against cardiolipin (false positives with SLE and infectious mono); (2) FTA-ABS (specific) detects anti-treponemal antibodies.
Term
How long does an Ixodes tick need to feed in order to transmit a sufficient inoculum for infection?
Definition
To transmit Borrelia burgdorferi, it takes about 24 hours. Check ECG! Can affect heart weeks after initial infection.
Term
Leptospirosis can cause Weil's syndrome, which is...?
Definition
Vasculitis w/ hemorrhagic complications, kidney damage w/ RF, & iver damage w/ jaundice.
Term
Pneumonia in a young person + cold hemagglutination='s?
Definition
Mycoplasma pneumoniae. Also: "fried-egg appearance" on 2-3 week's culture on Eaton's agar.
Term
What are the two obligate intracellular parasites and what is different about them?
Definition
Chlamydiae replicate within inclusion bodies, while Rickettsiae replicate freely in the cytoplasm. (Note that tx w/ doxycycline works b/c doxy enters cells!)
Term
What is the #1 STI in the US and why (probably)?
Definition
Chlamydia trachomatis! Probably b/c infections in males are usually clinically silent (but could cause Reiter's syndrome=arthritis+conjunctivitis, esp. in HLA-B27 pts).
Term
What 3 infections should you think of with a palm & sole rash?
Definition
(1) Rocky Mountain spotted fever; (2) Syphilis; (3) Coxsackievirus
Term
What is transmitted by the bite of the Dermacentor wood or dog tick?
Definition
RMSF (Rickettsia rickettsii), which is more common on the East Coast. The inoculum is sufficient only after 6-10 hours of tick feeding. The rash spreads proximally from the palms & soles.
Term
A patient develops a rash that spreads distally, sparing the palms, soles, & face. What is this?
Definition
Epidemic typhus (Rickettsia prowazekii). Louse-borne. Often epidemic during/following wars/natural disasters.
Term
What's special about Coxiella burnetti?
Definition
It's actually a Rickettsia, it can survive extracellularly as a spore, & it causes Q fever in individuals exposed to animal products (sheep, cattle, goats).
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