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Unit 6: Micro > Enteric Bacterial Infections 1: Major Foodborne Enterobacteriaceae > Flashcards

Enteric Bacterial Infections 1: Major Foodborne Enterobacteriaceae Flashcards

1
Q

Describe the cellular characteristics of Shigella

A
  • Gram (-) rods
  • Non-lactose fermenter
  • Non-H2S producing
  • Non-motile
  • Facultative
  • Intracellular
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2
Q

What are two other names for Shigella enterocolitis?

A

Bacillary Dysentery and Shigellosis

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3
Q

What is the difference in infectious dose between Shigella and Salmonella

A
  • Shigella - low dose
  • Salmonella - high dose
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4
Q

What human phenotype is associated with reactive arthritis from shigella (and other bugs)?

A

HLA-B27 phenotype

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5
Q

Describe the pathogenesis for shigella infection

A
  • Shigella engulfed by M cells
  • Bacteria survive macros and invade epithelium
  • Bacteria can transfer betwixt adjacent cells
  • Use T3SS to inject exotoxin
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6
Q

What is Shigella virulence dependent on?

A

Plasmid

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7
Q

What virulent genes are encoded on the Shigella plasmid?

A
  • Shiga toxin - Protein synthesis inhibition
  • Shu and Aerobactin - Ironchelating molecules
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8
Q

What are the major virulence factors for Shigella?

A
  • T3SS
  • IcsA - use of host actin to cross into neighboring cells
  • IpaB - induces macrophage apoptosis
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9
Q

What is a major risk of Shigella infection?

A

Hemolytic Uremic Syndrome

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10
Q

What age group(s) is/are affected most severely by Shigella?

A

Very young and old

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11
Q

What are the lab procedures for Shigella Dx?

A
  • Agglutination
  • Methylene BLue stain - fecal sample (determination of presence of neutrophils)
  • Blood smear - detect schistocytes for HUS
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12
Q

In the Tx of Shigella and E. coli, what is a very important consideration?

A

Shigella treat with ABs decrease HUS risk while Tx for E.coli with ABs is controversial

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13
Q

Tx procedure for mild and severe shigella?

A
  • Mild - fluid/electrolytes
  • Severe - Ceftriaxone, fluoroquinolone, azythromycin, cefiximine (NO fluroquins for children)
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14
Q

Describe the antimicrobial assay for Shigella

A
  • Shmear bacteria onto agar
  • Place AB-drenched filterpaper onto agar.
  • Incubate
  • Check zone of clearing with reference table
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15
Q

Describe the bacterial characteristics of E. coli

A
  • Straight Gram(-) rods
  • Facultative
  • Lactose fermentation
  • H2S negative
  • Urease negative
  • Mobile/Nonmobile (depending on strian)
  • Normal GI flora
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16
Q

Describe the use of MacConkey agar in IDing E. coli

A

The agar will turn bright pink because it ferments lactose (pink = lactose fermenter)

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17
Q

What strain of E. coli causes traveler’s diarrhea?

A

Enterotoxigenic E. coli (ETEC)

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18
Q

What type of E. coli causes hemorrhagic colitis/HUS?

A

Enterohemorrhagic E. coli (EHEC)

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19
Q

Describe the pathogenesis of Enterotoxigenic diarrhea

A
  • Pili attach to jejunum/ileum
  • Enterotoxin synthed
  • Enterotoxin causes efflux of ions
  • Host loses fluid - watery diarrhea
20
Q

Describe pathogenesis of Enterohemorrhagic diarrhea

A
  • Bac invade/destroy epi of large intestine
  • Inflamm
  • Bloody diarrhea
21
Q

What gene does O157:H7 E. coli carry?

A

Shigella gene for Shiga toxin

22
Q

Briefly describe the different modes of infection of ETEC, EPEC, EIEC, and EHEC

A
  • ETEC - Fimbriae adhere to cell and deliver enterotoxin
  • EPEC - Attach to cell using actin bundle (pedestal) and inject molecules using injection system
  • EIEC - Endocytosed by M Cell (similar mechanism to Shigella
  • EHEC - Actin bundle + Shiga toxin delivery via injection system
23
Q

What is ETEC? EPEC? EIEC? EHEC?

A

ET - Enterotoxigenic

EP - Enteropathogenic

EH - Enterohemorrhagic

EI - Enteroinvasive

E. coli

24
Q

What two subtypes of E. coli use injection systems?

A

Enteropathogenic and Enterohemorrhagic

25
Q

What strain of E. coli typically causes UTIs?

A

Uropathogenic

26
Q

What is the virulence factor for uropathogenic E. coli?

A

P. fimbriae

27
Q

What is a red flag for E. coli Enterocolitis?

A

Water diarrhea, bloody diarrhea (progression from the former to the latter)

28
Q

What is the culture procedure for E. coli?

A

Stool sample on blood agar and MacConkey agar (Pink for E. coli [lactose fermenter!])

29
Q

What is AB use associated with in Tx of EHEC?

A

Increased HUS risk

30
Q

Tx for Uropathogenic E. coli?

A
  • Simple - Trimethoprim sulfamethoxazole/ampicillin
  • Extended - third generation cephalosporin (cefotaxime)
31
Q

Cellular characteristics of Salmonella

A
  • Gram (-) rods
  • Motile
  • Oxidase and urease negative
  • H2S
  • Thousands of serovars
  • Acquired from contaminated food
32
Q

Typical size of infectious dose for Salmonella?

A

Large dose (compared to small dose in Shigella)

33
Q

Describe pathogenesis of Salmonella

A
  • M cell endocytoses Salmonella
  • a) Can destroy macrophages and infect epithelium on basal side
  • Spread thru adjacent cells
  • b) use macros as trojan horses and disseminate causing typhoid fever
34
Q

What are the virulence factors of Salmonella?

A
  • Ipf - enhances adhesion to M cell
  • T3SS
  • SipB - macro apoptosis
35
Q

What are additional virulence factors for S. typhi?

A
  • Spi Type 3 - remodels phagosomes for systemic spread
  • Vi antigen - capsule for immune evasion
36
Q

What is the risk of HUS for Salmonella infection?

A

There is no riskk

37
Q

What is the general mechanism for typhoid fever?

A
  • Salmonella (typhi or paratyphi) invade M cells
  • Disseminat thru macros
  • Once critical density reached, macros apoptose and escape into bloodstream
38
Q

In what organ does salmonella sequester?

A

Gallbladder

39
Q

What allele is protective against penetration of the gut?

A

CFTR cystic fibrosis allele (possibly why the gene has not disappeared from the gene pool)

40
Q

What is a sign on physical exam of typhoid fever?

A

Rose spots

41
Q

RFs for typhoid fever?

A
  • Corticosteroids
  • Immunosuppresion
  • Malignancy
  • Diabetes
42
Q

PE signs of Salmonella Enterocolitis?

A
  • Nonbloody diarrhea, fever, dehydration
43
Q

In addition to Tx, what should one do once salmonella has been Dx?

A

Inform local health authorities!

44
Q

What are tipoffs of typhoid fever?

A

Traveling abroad; Rose spots

45
Q

Tx for salmonella enteric fevers/septicemia?

A

Ceftriaxone/ciprofloxacin

Unit 6: Micro (13 decks)

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