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USMLE Step I Microbiology > Other Gram + Bacteria > Flashcards

Other Gram + Bacteria Flashcards

1
Q

properties of Enterococci

A
  • gram + cocci
  • catalase -
  • PYR +
  • variable hemolysis
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2
Q

Entercocci (E. faecalis and E. faecium):

where are they normal?

what are they resistant to?

what do they cause?

A
  • normal colonic flora
  • penicillin G resistant
  • cause:
    • UTI
    • biliary tract infections
    • subacute endocarditis (following GI/GU procedures)
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3
Q

what do vancomycin resistant enterococci (VRE) cause?

A
  • cause nosocomial infection
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4
Q

enterococci vs. nonenterococcal group D

A

enterococci are hardier than non enterococci group D

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5
Q

what do you grow enterococci in in the lab?

A
  • 6.5% NaCl and bile
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6
Q

properties of Bacillus anthracis

A
  • gram +
  • spore forming rod that produces anthrax toxin
  • ONLY bacterium with a polypeptide capsule (contains D-glutamate)
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7
Q

cutaneous anthrax

A
  • painless papule surrounded by vesicles –> ulcer with black eschar (painless, necrotic) –> uncommonly progresses to bacteremia and death
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8
Q

pulmonary anthrax

A
  • inhalation of spores –> flu like symptoms that rapidly progress to fever, pulmonary hemorrhage, mediastinitis, and shock
  • also known as woolsorter’s disease
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9
Q

properties of Bacillus cereus

A
  • gram + rod
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10
Q

what does Bacillus cereus cause?

A
  • food poisoning
  • “Reheated rice syndrome”
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11
Q

Bacillus cereus and Reheated Rice Syndrome

A
  • spores survive cooking rice
    • keeping rice warm results in germination of spores and enterotoxin formation
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12
Q

Bacillus cereus emetic type

A
  • usually seen with rice and pasta
  • nausea and vomiting within 1-5 hours
  • caused by cereulide–a preformed toxin
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13
Q

Bacillus cereus diarrheal type

A
  • causes watery, nonbloody diarrhea and GI pain within 8-18 hours
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14
Q

properties of Clostridia (with exotoxins)

A
  • gram +
  • spore forming
  • oligate anaerobic rods
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15
Q

C. tetani–toxin and mechanism

A
  • toxin: tetanospasmin–an exotoxin causing tetanus
  • tetanus toxin (and botulinum toxin) are proteases that cleave SNARE proteins for neurotransmitters
    • blocks release of inhibitor neurotransmitters, GABA and glycine, from Renshaw cells in the spinal cord
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16
Q

C. tetani–effects

A
  • tetanospasmin causes
    • spastic paralysis
      • “tetanus is tetanic paralysis”
    • trismus (lockjaw)
    • risus sardonicus–raised eyebrows and open grin
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17
Q

C. tetani:

how to prevent?

how to treat?

A
  • prevention:
    • tetanus vaccine
  • treatment:
    • antitoxin +/- vaccine booster
    • diazepam–for muscle spasms
    • wound debridement
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18
Q

C. botulinum–toxin and mechanism

A
  • toxin: heat labile toxin–botulinum toxin
  • mechanism:
    • inhibits ACh release at the neuromuscular junction, causing botulism
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19
Q

C. botulinum:

in adults?

in babies?

A
  • adults:
    • disease is caused by ingestion of preformed toxin
  • babies:
    • ingestion of spores (ie. in honey) leads to disease
      • Floppy Baby Syndrome
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20
Q

C. botulinum–treatment

A
  • antitoxin
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21
Q

where does C. botulinum come from?

A
  • Botulinum is from bad bottles of food, juice, honey
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22
Q

C. botulinum–effects

A
  • flaccid paralysis
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23
Q

C. botulinum and botox

A
  • local botox injections used to treat foca ldystonia, achalasia, and muscle spasms
  • also used for cosmetic reduction of facial wrinkles
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24
Q

C. perfringens–toxin, effects

A
  • produce alpha toxin (lecithinase, a phospholipase)
    • spores can survive in undercooked food
      • so, when ingested, bacteria release heat labile enterotoxin –> food poisoning
  • can cause myonecrosis (gas gangrene) and hemolysis
    • “Perfringens perforates a gangrenous leg”
25
*C. difficile*--diagnosis
* diagnosis by detecting one or both toxins in stool by PCR
26
*C. difficile*--toxin
* 2 possible toxins * toxin A--enterotoxin * toxin B--cytotoxin
27
*C. difficile* toxin A
* enterotoxin * binds ot the brush border of the gut
28
*C. difficile* toxin B
* cytotoxin * causes cytoskeletal disruption via actin depolymerization --\> diarrhea --\> pseudomembranous colitis
29
what is often the cause of *C. difficile* infection?
* often the *C. difficile* infection is secondary to antibiotic use, especially clindamycin or ampicillin * associated with PPI use
30
*C. diffiicile*--effects
* diarrhea * "***Di**fficile* causes **di**arrhea"
31
*C. difficile*--treatment
* metronidazole or oral vancomycin * for recurrent cases, consider repeating prior regimen, fidazomicin, or fecal microbiota transplant
32
properties and mechanism of *Corynebacterium diphtheriae*
* gram + rod * "coryne = club shaped" * potent exotoxin inhibits protein synthesis via ADP ribosylation of EF-2 * "**ABCDEFG**" * **A**DP ribosylation * **B**eta prophage * ***C**orynebacterium* * ***D**iphtheriae* * **E**longation **F**actor 2 * **G**ranules
33
what does *Corynebacterium diphtheriae* cause and how?
* diphtheria via exotoxin encoded by beta prophage
34
*Corynebacterium diphtheriae* infection--effects
* pseudomembranous pharyngitis (grayish white membrane) * lymphadenopathy * myocarditis * arrhythmias
35
*Corynebacterium diphtheriae*--diagnosis
* lab diagnosis based on gram + rods with metachromatic (blue and red) granules and + Elek test for toxin
36
how to prevent diphtheria?
toxoid vaccine
37
what medium do you use to grow *Corynebacterium diphtheriae?* what do the colonies look like?
* cystine tellurite agar * black colonies
38
properties and mechanism of *Listeria monocytogenes*
* gram + * facultative anaerobe rod * form "rocket tails" via actin polymerization that allow intracelllar movement and cell to cell spread across cell membranes, therby avoiding antibody * characteristic tumbling motility in broth
39
how does one acquire a *Listeria monocytogenes* infection?
* acquired by ingestion of unpasteurized dairy products and cold deli meats * via transplacental transmission * by vaginal transmission during birth
40
what does *Listeria monocytogenes* cause?
* amnionitis * septicemia * spontaneous abortion in pregnant women * granulomatosis infantiseptica * neonatal meningitis * meningitis in immunocompromised patients * mild, self-limited gastroenteritis in healthy individuals
41
*Listeria monocytogenes*--treatment
* ampicillin in infants, immunocompromised, and the elderly as empirical treatment of meningitis
42
how are *Nocardia* and *Actinomyces* alike?
* both are gram + and form long, branching filaments resembling fungi *
43
*Nocardia* and *Actinomyces--*differences in their properties and mechanisms
* Nocardia * aerobe * acid fast (weak) * found in soil * Actinomyces * anaerobe * not acid fast * normal oral, reproductive, and GI flora
44
*Nocardia* and *Actinomyces*--differences in what they cause and treatments?
* Nocardia * can cause: * pulmonary infections in immunocompromised (can mimic TB but with -PPD) * cutaneous infections after trauma in immunocompetent * treatment: * sulfonamides (TMP-SMX) * Actinomyces * can cause: * oral/facial abscesses that drain thru sinus tracts * forms yellow "sulfur granules" * can also cause PID with IUDs * treatment: * penicillin * "Treatment is a **SNAP**: **S**ulfonamides--***N****ocardia;* ***A**ctinomyces*--**P**encillin"
45
primary and secondary tuberculosis
* PPD + if current infection or past exposure * PPD - if no infection and in sarcoidosis * Interferon gamma release assay (IGRA) has fewer false positives from BCG vaccination * causeating granulomas with central necrosis and Langerhans giant cells are characteristic of 2ndary tuberculosis
46
name the types of Mycobacteria
* *Mycobacterium tuberculosis* * *M. avium*--*intracellulare* * *M. scrofulaceum* * *M. marinum*
47
what does *M. tuberculosis* cause?
* TB * often resistant to multiple drugs
48
what does *M. avium--intracellulare* cause? what is the prophylaxis?
* disseminated, non TB disease in AIDS * often resistant to multiple drugs * prophylaxis with azithromycin when CD4+ count \< 50 cells/mm3
49
what does *M. scrofulaceum* cause?
* cervical lymphadenitis in children
50
what does *M. marinum* cause?
* hand infection in aquarium handlers
51
tuberculosis--symptoms
* fever * night sweats * weight loss * cough--nonproductive or productive * hemolysis
52
cord factor and mycobacteria
* cord factor creates a "serpentine cord" appearance in virulent *M. tuberculosis* strains * inhibits macrophage maturation * induces release of TNF alpha * sulfatides (surface glycolipids) inhibit phagolysosomal fusion
53
properties of Mycobacteria
* all are acid fast * pink rods at arrow tips
54
what bacterium causes Leprosy (Hansen disease)?
* *Mycobacterium leprae*
55
properties of *Mycobacterium leprae*
* acid fast bacillus that like cool temperatures * infects skin and superficial nerves--"glove and stocking" loss of sensation * cannot be grown in vitro * reservoid in the US: armadillos
56
2 forms of Leprosy (Hansen disease)
* lepromatous * tuberculoid
57
explain lepramatous Hansen disease
* presents diffusely over the skin, with leonine (lion-like) facies * is communicable * characterized by low cell mediated immunity with a humoral Th2 response * "**L**epromatous form can be **L**ethal"
58
explain tuberculoid Hansen disease
* limited to a few hypoesthetic, hairless skin plaques * characterized by high cell mediated immunity with a largely Th1 type immune response
59
what are the treatments for each form of Hansen disease?
* tuberculoid form: * dapsone * rifampin * lepromatous form: * same as tuberculoid * BUT add clofazimine

USMLE Step I Microbiology (44 decks)

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