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USMLE Step I Microbiology > Gram - Rods > Flashcards

Gram - Rods Flashcards

1
Q

properties and virulence factors of of E. coli

A
  • gram - rods
  • virulence factors:
    • fimbriae
    • K capsule
    • LPS endotoxin
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2
Q

what can the fimbriae virulence factor of E. coli cause?

A
  • cystitis
  • pyelonephritis
    • P-pili
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3
Q

what can the K capsule virulence factor of E. coli cause?

A
  • pneumonia
  • neonatal meningitis
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4
Q

what can the LPS endotoxin of E. coli cause?

A
  • septic shock
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5
Q

name the 4 strains of E. coli

A
  • EIEC
  • ETEC
  • EPEC
  • EHEC
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6
Q

EIEC–toxin and mechanism

A
  • microbe invades intestinal mucosa
    • causes necrosis and inflammation
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7
Q

EIEC–presenation

A
  • Invasive
  • dysentery
  • clinical manifestation similar to Shigella
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8
Q

ETEC–toxin and mechanis

A
  • produces heat labile and heat stable enteroToxins
  • no inflammation or invasion
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9
Q

ETEC–presentation

A
  • Traveler’s diarrhea–watery
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10
Q

EPEC–toxin and mechanism

A
  • no toxin produced
  • adheres to apical surface, flattens villi, and prevents absorption
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11
Q

EPEC–presentation

A
  • diarrhea
    • usually in children (Pediatrics)
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12
Q

EHEC–toxin and mechanism

A
  • O157:H7 is most common serotype in US
  • often transmitted via undercooked meat, raw leafy vegetables
  • shiga like toxin
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13
Q

Shiga like toxin of EHEC causes what?

give the symptoms and mechanism

A
  • hemolytic uremic syndrome
    • causes triad of anemia, thrombocytopenia, and acute renal failure due to microthombi forming on damaged endothelium –> mehanical hemolysis (with schistocytes on peripheral blood smear), platelet consumption, and dec renal blood flow
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14
Q

EHEC–presentation

A
  • dysentery–toxin alone causes necrosis and inflammation
    • “Hemorrhagic, Hamburgers, Hemolytic uremia syndrome”
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15
Q

what distinguishes EHEC from other E. coli?

A
  • EHEc does not ferment sorbitol
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16
Q

properties of Klebsiella

A
  • gram - rod
  • very mucoid colonies caused by abundant polysaccharide capsules
  • dark red “currant jelly” sputum–blood/mucus
  • intestinal flora
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17
Q

what does Klebsiella cause?

A
  • causes lobar pneumonia in alcoholics and diabetics when aspirated
    • 4 A’s of KlebsiellA
      • Aspiration pneumonia
      • Abscess in lungs and liver
      • Alcoholics
      • diAbetics
  • also causes nosocomial UTIs
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18
Q

Salmonella and Shigella–what is common to both?

A
  • gram - rods
  • non lactose fermenters
  • oxidase -
  • can invade the GI tract via M cells of Peyer patches
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19
Q

Salmonella typhi–reservoir

A
  • humans only
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20
Q

Salmonella typhi–spread

A
  • can disseminate hematogenously
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21
Q

Salmonella typhi–is H2S produced?

A
  • YES
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22
Q

Salmonella typhi–do they have flagella?

A
  • YES
    • “salmon swim”
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23
Q

Salmonella typhi–virulence factors

A
  • endotoxin
  • Vi capsule
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24
Q

Salmonella typhi–infectious dose (ID50)

A
  • high
    • large inoculum required b/c organism inactivated by gastric acids
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25
*Salmonella typhi*--effect of antibiotics on fecal excretion
* prolongs duration
26
*Salmonella typhi*--immune response
* primarily monocytes
27
*Salmonella typhi*--GI manifestations
* constipation * followed by diarrhea
28
*Salmonella typhi*--vaccine
* oral vaccine contains live attenuated *S. typhi* * IM vaccine contains Vi capsular polysaccharide
29
*Salmonella typhi*--unique properties
* causes typhoid fever * rose spots on abdomen, constipation, abdominal pain, fever * treat with ceftriaxone or fluoroquinolone * carrier state with gallbladder colonization
30
*Salmonella spp.* (except *S. typhi*)--reservoir
* humans * animals
31
*Salmonella spp.* (except *S. typhi*)--spread
* can disseminate heatogenously
32
*Salmonella spp.* (except *S. typhi*)--is H2S produced?
* YES
33
***Salmon****ella spp.* (except *S. typhi*)--flagella
* YES * "**salmon swim**"
34
*Salmonella spp.* (except *S. typhi*)--virulence factors
* endotoxin
35
*Salmonella spp.* (except *S. typhi*)--infectious dose ID50
* high
36
*Salmonella spp.* (except *S. typhi*)--effects of antibiotics on fecal excretion
* prolongs duration
37
*Salmonella spp.* (except *S. typhi*)--immune response
* PMNs in disseminated disease
38
*Salmonella spp.* (except *S. typhi*)--GI manifestations
* diarrhea * possibly bloody
39
*Salmonella spp.* (except *S. typhi*)--vaccine
* no vaccine
40
*Salmonella spp.* (except *S. typhi*)--unique manifestations
* poultry, eggs, pets, turtles are common sources * antibiotics not indicated * gastroenteritis is urually caused by non-typhoidal *Salmonella*
41
*Shigella*--reservoirs
* humans only
42
*Shigella*--spread
* cell to cell * no hematogenous spread
43
*Shigella*--is H2S produced?
* NO
44
*Shigella*--flagella
* NO
45
*Shigella*--virulence factors
* endotoxin * Shiga toxin (enterotoxin)
46
*Shigella*--infectious dose ID50
* low * very small inoculum required * resistant to gastric acids
47
*Shigella*--effect of antibiotics on excretion
* shortens duration
48
*Shigella*--immune response
* primarily PMN infiltration
49
*Shigella*--GI manifestations
* bloody diarrhea * bacillary dysentery
50
*Shigella*--vaccine
* no vaccine
51
*Shigella*--unique properties
* **Four F**'s * **F**ingers * **F**lies * **F**ood * **F**eces
52
*Shigella-*-in order of decreasing severity (less toxin produced)
* *S. dysenteriae* * *S. flexneri* * *S. boydii* * *S. sonnei*
53
*Shigella*--what is the key to pathogenicity?
* invasion is the key to pathogenicity * organisms that produce less toxin can cause disease due to invasion
54
properties of *Haemophilus influenzae*
* small gram - (coccobacillary) rod * aerosol transmission * produces IgA protease * culture on chocolate agar which contains factors V (NAD+) and X (hematin) for growth * can also be grown with *S. aureus* * which provides factor V thru hemolysis of RBCs
55
what does *Haemophilus influenze* cause? what strain is the most common cause of these infections
* non typeable (unencapsulated) strains are the most common of: * mucosal infections: * otitis media * conjunctivitis * bronchitis * invasive infections * since the vaccine for capsular type b was introduced * DOES NOT cause the flu * *Ha**EMOP**hilus* causes: * **E**piglottitis--can be charry red in children, thumbprint sign on x ray * **M**eningitis * **O**titis media * **P**neumonia
56
*Haemophilus influenzae*--treatment for: mucosal infections meningitis prophylaxis
* amoxicillin +/- claculanate for mucosal infections * ceftriaxone for meningitis * rifampin prophylaxis for close contacts
57
*Haemophilus influenzae*--vaccine
* vaccine contains type b capsular polysaccharide and PRP (polyribosylribitol phosphate) * conjugated in diphtheria toxoid or other protein * given between 2 and 18 mos of age
58
properties of *Legionella pneumophila*
* gram - rod * gram stains poorly, so use **silver** stain * grow on **charcoal** yeast extract medium with **iron** and **cysteine** * aerosol transmission from environmental water source habitat (ie. air conditioning systems, hot water tanks) * no person to person transmission * "think of a French **legionnarie** (soldier) with his **silver** helmet, sitting around a campfire (**charcoal**) with his (**iron**) dagger--he is no **sissy** (cysteine)"
59
*Legionella pneumophila*--detection
* detected by presence of antigen in urine * labs may show hyponatremia
60
what can *Legionella pneumophila* cause?
* **Legionnaires**' disease * Pontiac fever
61
Legionnaries' disease
* caused by *Legionella pneumophila* * severe pneumonia (often unilateral and lobar) * fever * GI symptoms * CNS symptoms * common in smokers and in chronic lung disease
62
Pontiac fever
* mild flu like syndrome
63
properties of *Pseudomonas aeruginosa*
* aerobic * ***Aer****uginosa--***aer**obic * motile * gram - rod * non lactose fermenting * oxidase + * produces pyocyanin (blue green pigment) * has a grape like odor * produces endotoxin (fever, shock), exotoxin A (inactivates EF-2), phospholipase C (degrades cell membranes), and pyocyanin (generates reactive oxygen species) * ferquently found in water --\> hot tub folliculitis
64
*Pseudomonas aeruginosa* is associated with:
* **PSEUDOMONAS** * **P**neumonia, pyocyanin * **S**epsis * **E**cthyma gangrenosum * **U**TIs * **D**iabetes, drug use * **O**steomyelitis--ie. puncture wounds * **M**ucoid polysaccharide capsule * **O**titis externa (swimmer's ear) * **N**osocomial infections--catheters equipment * exotoxin **A** * **S**kin infections (hot tub folliculitis)
65
*Pseudomonas aeruginosa*--treatment
* **CAMPFIRE** * **​C**arbapenems * **A**minoglycosides * **M**onobactams * **P**olymyxins--polymyxin B, colistin * **F**luoroquinolones--ciprofloxacin, levofloxacin * Th**IR**d and fourth generation cephalosporins--ceftazidime, cefepime * **E**xtended spectrum penicillins--piperacillin, ticarcillin
66
*Pseudomonas aeruginosa* and mucoid polysaccharide capsule
* mucoid polysaccharide capsule may contribute ot chronic pneumonia in cystic fibrosis patients due to biofilm formation
67
what can *Pseudomonas aeruginosa* cause?
* chronic pneumonia in cystic fibrosis patients * can cause wound infection in burn victims * hot tub folliculitis
68
ecthyma gangrenosum
* rapidly progressive, necrotic cutaneous lesion * caused by *Pseudomonas* bacteremia * typically seem in immunocompromised patients
69
properties of *Yersinia enterocolitica*
* gram - rod * usually transmitted from pet feces (puppies), contaminated milk, or pork
70
what can *Yersinia enterocolitica* cause?
* acute diarrhea * pseudoappendicitis (right lower abdominal pain due to mesenteric adenitis and/or terminal ileitis)
71
properties of *Helicobacter pylori*
* curved * terminally flagellated * gram - rod * triple + * catalase + * oxidase + * urease + * colonizes mainly antrum of stomach
72
*Helicobacter pylori*--diagnosis
* can use urea breath test or fecal antigen test for diagnosis
73
*H. pylori* and urease
* urease + * urease produces ammonia * creates an alkaline environment which helps *H. pylori* survive in acidic mucosa
74
what does *H. pylori* cause?
* gastritis * peptic ulcers--espcially duodenal
75
what is *H. pylori* a risk factor for?
* peptic ulcer disease * gastric adenocarcinioma * MALT lymphoma
76
*Helicobacter pylori*--treatment
* most common initial treatment is **triple** therapy: * **A**moxicillin * metronidazole if penicillin allergy * **C**larithromycin * **P**roton pump inhibitor * "**A**ntibiotics **C**ure ***P****ylori"*

USMLE Step I Microbiology (44 decks)

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