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USMLE Step I Microbiology > Gram - Rods > Flashcards

Gram - Rods Flashcards

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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
Q

Salmonella typhi–effect of antibiotics on fecal excretion

A
  • prolongs duration
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26
Q

Salmonella typhi–immune response

A
  • primarily monocytes
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27
Q

Salmonella typhi–GI manifestations

A
  • constipation
    • followed by diarrhea
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28
Q

Salmonella typhi–vaccine

A
  • oral vaccine contains live attenuated S. typhi
  • IM vaccine contains Vi capsular polysaccharide
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29
Q

Salmonella typhi–unique properties

A
  • causes typhoid fever
    • rose spots on abdomen, constipation, abdominal pain, fever
    • treat with ceftriaxone or fluoroquinolone
  • carrier state with gallbladder colonization
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30
Q

Salmonella spp. (except S. typhi)–reservoir

A
  • humans
  • animals
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31
Q

Salmonella spp. (except S. typhi)–spread

A
  • can disseminate heatogenously
32
Q

Salmonella spp. (except S. typhi)–is H2S produced?

A
  • YES
33
Q

Salmonella spp. (except S. typhi)–flagella

A
  • YES
    • “salmon swim”
34
Q

Salmonella spp. (except S. typhi)–virulence factors

A
  • endotoxin
35
Q

Salmonella spp. (except S. typhi)–infectious dose ID50

A
  • high
36
Q

Salmonella spp. (except S. typhi)–effects of antibiotics on fecal excretion

A
  • prolongs duration
37
Q

Salmonella spp. (except S. typhi)–immune response

A
  • PMNs in disseminated disease
38
Q

Salmonella spp. (except S. typhi)–GI manifestations

A
  • diarrhea
    • possibly bloody
39
Q

Salmonella spp. (except S. typhi)–vaccine

A
  • no vaccine
40
Q

Salmonella spp. (except S. typhi)–unique manifestations

A
  • poultry, eggs, pets, turtles are common sources
  • antibiotics not indicated
  • gastroenteritis is urually caused by non-typhoidal Salmonella
41
Q

Shigella–reservoirs

A
  • humans only
42
Q

Shigella–spread

A
  • cell to cell
  • no hematogenous spread
43
Q

Shigella–is H2S produced?

A
  • NO
44
Q

Shigella–flagella

A
  • NO
45
Q

Shigella–virulence factors

A
  • endotoxin
  • Shiga toxin (enterotoxin)
46
Q

Shigella–infectious dose ID50

A
  • low
    • very small inoculum required
    • resistant to gastric acids
47
Q

Shigella–effect of antibiotics on excretion

A
  • shortens duration
48
Q

Shigella–immune response

A
  • primarily PMN infiltration
49
Q

Shigella–GI manifestations

A
  • bloody diarrhea
    • bacillary dysentery
50
Q

Shigella–vaccine

A
  • no vaccine
51
Q

Shigella–unique properties

A
  • Four F’s
    • Fingers
    • Flies
    • Food
    • Feces
52
Q

Shigella--in order of decreasing severity (less toxin produced)

A
  • S. dysenteriae
  • S. flexneri
  • S. boydii
  • S. sonnei
53
Q

Shigella–what is the key to pathogenicity?

A
  • invasion is the key to pathogenicity
    • organisms that produce less toxin can cause disease due to invasion
54
Q

properties of Haemophilus influenzae

A
  • 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
Q

what does Haemophilus influenze cause?

what strain is the most common cause of these infections

A
  • 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
  • HaEMOPhilus causes:
    • Epiglottitis–can be charry red in children, thumbprint sign on x ray
    • Meningitis
    • Otitis media
    • Pneumonia
56
Q

Haemophilus influenzae–treatment for:

mucosal infections

meningitis

prophylaxis

A
  • amoxicillin +/- claculanate for mucosal infections
  • ceftriaxone for meningitis
  • rifampin prophylaxis for close contacts
57
Q

Haemophilus influenzae–vaccine

A
  • 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
Q

properties of Legionella pneumophila

A
  • 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
Q

Legionella pneumophila–detection

A
  • detected by presence of antigen in urine
  • labs may show hyponatremia
60
Q

what can Legionella pneumophila cause?

A
  • Legionnaires’ disease
  • Pontiac fever
61
Q

Legionnaries’ disease

A
  • caused by Legionella pneumophila
  • severe pneumonia (often unilateral and lobar)
  • fever
  • GI symptoms
  • CNS symptoms
  • common in smokers and in chronic lung disease
62
Q

Pontiac fever

A
  • mild flu like syndrome
63
Q

properties of Pseudomonas aeruginosa

A
  • aerobic
    • Aeruginosa–aerobic
  • 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
Q

Pseudomonas aeruginosa is associated with:

A
  • PSEUDOMONAS
    • Pneumonia, pyocyanin
    • Sepsis
    • Ecthyma gangrenosum
    • UTIs
    • Diabetes, drug use
    • Osteomyelitis–ie. puncture wounds
    • Mucoid polysaccharide capsule
    • Otitis externa (swimmer’s ear)
    • Nosocomial infections–catheters equipment
    • exotoxin A
    • Skin infections (hot tub folliculitis)
65
Q

Pseudomonas aeruginosa–treatment

A
  • CAMPFIRE
    • ​Carbapenems
    • Aminoglycosides
    • Monobactams
    • Polymyxins–polymyxin B, colistin
    • Fluoroquinolones–ciprofloxacin, levofloxacin
    • ThIRd and fourth generation cephalosporins–ceftazidime, cefepime
    • Extended spectrum penicillins–piperacillin, ticarcillin
66
Q

Pseudomonas aeruginosa and mucoid polysaccharide capsule

A
  • mucoid polysaccharide capsule may contribute ot chronic pneumonia in cystic fibrosis patients due to biofilm formation
67
Q

what can Pseudomonas aeruginosa cause?

A
  • chronic pneumonia in cystic fibrosis patients
  • can cause wound infection in burn victims
  • hot tub folliculitis
68
Q

ecthyma gangrenosum

A
  • rapidly progressive, necrotic cutaneous lesion
  • caused by Pseudomonas bacteremia
  • typically seem in immunocompromised patients
69
Q

properties of Yersinia enterocolitica

A
  • gram - rod
  • usually transmitted from pet feces (puppies), contaminated milk, or pork
70
Q

what can Yersinia enterocolitica cause?

A
  • acute diarrhea
  • pseudoappendicitis (right lower abdominal pain due to mesenteric adenitis and/or terminal ileitis)
71
Q

properties of Helicobacter pylori

A
  • curved
  • terminally flagellated
  • gram - rod
  • triple +
    • catalase +
    • oxidase +
    • urease +
  • colonizes mainly antrum of stomach
72
Q

Helicobacter pylori–diagnosis

A
  • can use urea breath test or fecal antigen test for diagnosis
73
Q

H. pylori and urease

A
  • urease +
  • urease produces ammonia
    • creates an alkaline environment which helps H. pylori survive in acidic mucosa
74
Q

what does H. pylori cause?

A
  • gastritis
  • peptic ulcers–espcially duodenal
75
Q

what is H. pylori a risk factor for?

A
  • peptic ulcer disease
  • gastric adenocarcinioma
  • MALT lymphoma
76
Q

Helicobacter pylori–treatment

A
  • most common initial treatment is triple therapy:
    • Amoxicillin
      • metronidazole if penicillin allergy
    • Clarithromycin
    • Proton pump inhibitor
      • “Antibiotics Cure Pylori”

USMLE Step I Microbiology (44 decks)

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