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Microbiology > Enterobacteria > Flashcards

Enterobacteria Flashcards

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1
Q

enterobacteriaceae cell morphology

A

moderate-size gram-negative rods; non-spore-forming; motile

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2
Q

enterobacteriaceae physiology

A

all are facultative anaerobes

ferment glucose
reduce nitrates to nitrites

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3
Q

distinguishing metabolic characteristics

A

oxidase negative
lactose fermentation
resistance to bile salts
indole test

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4
Q

oxidase negative

A

do not have cytochrome C oxidase; distinguishes pseudomonas (+) from other gram-negative rods (-)

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5
Q

lactose fermentation

A

red colonies on MacConkey agar
dark colonies (with a green sheen) on EMB agar
distinguishes lactose-fermenting from lactose non-fermenting

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6
Q

resistance to bile salts

A

growth with bile salts
shigella is resistant
salmonella is sensitive

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7
Q

indole test

A

tryptophanase converts tryptopha to indole (red with Kovac’s reagent)

e.coli (+) vs enterobacter sp (-)

distinguishes between different species

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8
Q

enterobacteriaceae ecology

A

found worldwide in soil, water, vegetation and microbial flora of animals and humans; some are always associated with disease; some are normal flora that can become pathogens

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9
Q

clinical presentations of enteric infections

A 
GI infections (watery diarrhea)
dysentery (bloody diarrhea)
skin and wound infections
enteric fever/typhoid fever
septicemia (blood infection)
meningitis (inflammation, infection of fluid around brain and spine)
UTIs
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10
Q

enteric diarrhea

A

2nd leading cause of death among children 5 or younger in developing countries

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11
Q

diseases caused by e. coli

A

neonatal meningitis causing E. coli (NMEC)

UTIs - UPEC; usually acquired from hospitals

gastroenteritis - category B pathogen; 300,000 deaths/yr

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12
Q

enterotoxigenic (ETEC)

A

traveler’s diarrhea

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13
Q

ETEC mechanism

A

mediated by heat-labile enterotoxin (like cholera) and heat-stable enterotoxin; activate guanylate cyclase and stimulate secretion of fluid

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14
Q

EHEC/ STEC

A

produces cytotoxin (verotoxin) - called shiga-like toxin; severe abdominal pain, bloody diarrhea, low fever (or no fever); low infectious dose (<100 viable bacteria can cause disease); treatment with antibiotics is contraindicated

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15
Q

hemolytic uremic syndrom

A

(EHEC/STEC) causes acute renal failure - toxin causes death of endothelial cells of glomeruli and afferent arterioles, reducing glomerular filtration, and causing kidney tissue necrosis

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16
Q

EPEC

A

childhood diarrhea; organism adheres to enterocyte plasma membrane and causes destruction of microvilli producing watery diarrhea; adhesiveness mediated by plasmid-encoded pilus; infants less than 1 year affected

17
Q

EHEC

A

responds to quorum sensing signals

18
Q

EAEC

A

causes inflammatory, water and often persisten diarrhea; persistent and acute diarrhea in children; commonly isolated from patients with traveller’s diarrhea; HIV-positive patients with diarrhea; asymptomatic infection; strain heterogeneity; host susceptibility

19
Q

enteroinvasive (EIEC)

A

mechanism is more related to shigella than other pathovars of e. coli

invades and destroys colonic epithelium; fever/cramps/bloody diarrhea; uncommon; oftenn foodborne

20
Q

Shigella

A

most common cause of dysentry and persistent diarrhea

21
Q

shigella properties

A

aerobic, non-motile, glucose-fermenting, gram-negative rods; low infectious dose (as few as 10 cells, ~500,000 infectious doses fit on a pin head); spread by fecal-oral contact; invade colonic epithelium; produce enterotoxins that can be cytotoxic (shiga-toxin and serine protease autotransporters)

22
Q

shigella species

A 
shigella sonnei (most common in US)
shigella flexneri (mostly in developing countries)
shigella boydii (not see much in the US, mostly in developing countries)
shigella dysenteriae (severe, episodic outbreaks in developing countries)
23
Q

shigella incubation time

A

symptoms begin 1-2 days after exposure

24
Q

shigella clinical symptoms

A

abdominal cramps, diarrhea, fever, bloody stools

25
Q

shigella sonnei/shigella flexneri

A

pediatric disease (1-4 years old); associated with daycare centers, schools, and custodial institutions; spread by fecal-oral route (not washing hands); low infectious dose: <50 bacilli can establish disease

26
Q

s. dysenteriae virulence

A

type 1 virulence factor: shiga toxin; irreversibly inactivates mammalian 60S ribosomal subunit; stops protein synthesis; targets sodium absorptive villus cell; produces decrease in sodium absorption; more fluid accumulates in lumen; cytotoxic: kills intestinal epithelial and endothelial cells yielding bloody diarrhea

27
Q

shigella pathogenesis

A

colonizes small intestine and multipies during first 12 hours; initial sign of infection is profuse watery diarrhea without histological evidence of mucosal invasion; mediated by enterotoxin; invasion of colonic epithelium results in lower abdominal cramps, difficulty defecating, abundant pus, and blood in stool; bacteremia is uncommon

28
Q

s. sonnei pathogenesis

A

has the same invasion process as other species, but with no dysentery only watery diarrhea

29
Q

s. dysenteriae type 1

A

most sever possibly due to intensity of inflammatory response

30
Q

s. flexneri

A

causes severe illness with dysentery and bloody diarrhea; has no genes for shiga toxin

31
Q

salmonella characteristics

A

non-motile, gram-negative, non-spore-forming rod

32
Q

solmonella enterica sources of infection

A

contact with animals; ingestion of contaminated water, food; by fecal-oral contact in children

33
Q

enteric fever

A

typhoid fever

34
Q

typhoid fever

A

average incubation period is 10-14 days, up to 60 days; gradually increasing high fever; rash, headach, abdominal pain, malaise, and decreased appetite; symptoms typically persist for a few days, fewer can continue for weeks to months without treatment; severe cases result in intestinal perforation; treated with antibioitcs (increasing antibiotic resitance)

carrier state can develop

35
Q

gastroenteritis

A

more common disease of salmonella infections; more acid sensitive than shigella; septicemia in pediatric and geriatric patients

Microbiology (15 decks)

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