Enteric Bacterial Infections 1: Major Foodborne Enterobacteriaceae Flashcards
Describe the cellular characteristics of Shigella
- Gram (-) rods
- Non-lactose fermenter
- Non-H2S producing
- Non-motile
- Facultative
- Intracellular
What are two other names for Shigella enterocolitis?
Bacillary Dysentery and Shigellosis
What is the difference in infectious dose between Shigella and Salmonella
- Shigella - low dose
- Salmonella - high dose
What human phenotype is associated with reactive arthritis from shigella (and other bugs)?
HLA-B27 phenotype
Describe the pathogenesis for shigella infection
- Shigella engulfed by M cells
- Bacteria survive macros and invade epithelium
- Bacteria can transfer betwixt adjacent cells
- Use T3SS to inject exotoxin
What is Shigella virulence dependent on?
Plasmid
What virulent genes are encoded on the Shigella plasmid?
- Shiga toxin - Protein synthesis inhibition
- Shu and Aerobactin - Ironchelating molecules
What are the major virulence factors for Shigella?
- T3SS
- IcsA - use of host actin to cross into neighboring cells
- IpaB - induces macrophage apoptosis
What is a major risk of Shigella infection?
Hemolytic Uremic Syndrome
What age group(s) is/are affected most severely by Shigella?
Very young and old
What are the lab procedures for Shigella Dx?
- Agglutination
- Methylene BLue stain - fecal sample (determination of presence of neutrophils)
- Blood smear - detect schistocytes for HUS
In the Tx of Shigella and E. coli, what is a very important consideration?
Shigella treat with ABs decrease HUS risk while Tx for E.coli with ABs is controversial
Tx procedure for mild and severe shigella?
- Mild - fluid/electrolytes
- Severe - Ceftriaxone, fluoroquinolone, azythromycin, cefiximine (NO fluroquins for children)
Describe the antimicrobial assay for Shigella
- Shmear bacteria onto agar
- Place AB-drenched filterpaper onto agar.
- Incubate
- Check zone of clearing with reference table
Describe the bacterial characteristics of E. coli
- Straight Gram(-) rods
- Facultative
- Lactose fermentation
- H2S negative
- Urease negative
- Mobile/Nonmobile (depending on strian)
- Normal GI flora
Describe the use of MacConkey agar in IDing E. coli
The agar will turn bright pink because it ferments lactose (pink = lactose fermenter)
What strain of E. coli causes traveler’s diarrhea?
Enterotoxigenic E. coli (ETEC)
What type of E. coli causes hemorrhagic colitis/HUS?
Enterohemorrhagic E. coli (EHEC)
Describe the pathogenesis of Enterotoxigenic diarrhea
- Pili attach to jejunum/ileum
- Enterotoxin synthed
- Enterotoxin causes efflux of ions
- Host loses fluid - watery diarrhea
Describe pathogenesis of Enterohemorrhagic diarrhea
- Bac invade/destroy epi of large intestine
- Inflamm
- Bloody diarrhea
What gene does O157:H7 E. coli carry?
Shigella gene for Shiga toxin
Briefly describe the different modes of infection of ETEC, EPEC, EIEC, and EHEC
- 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
What is ETEC? EPEC? EIEC? EHEC?
ET - Enterotoxigenic
EP - Enteropathogenic
EH - Enterohemorrhagic
EI - Enteroinvasive
E. coli
What two subtypes of E. coli use injection systems?
Enteropathogenic and Enterohemorrhagic
What strain of E. coli typically causes UTIs?
Uropathogenic
What is the virulence factor for uropathogenic E. coli?
P. fimbriae
What is a red flag for E. coli Enterocolitis?
Water diarrhea, bloody diarrhea (progression from the former to the latter)
What is the culture procedure for E. coli?
Stool sample on blood agar and MacConkey agar (Pink for E. coli [lactose fermenter!])
What is AB use associated with in Tx of EHEC?
Increased HUS risk
Tx for Uropathogenic E. coli?
- Simple - Trimethoprim sulfamethoxazole/ampicillin
- Extended - third generation cephalosporin (cefotaxime)
Cellular characteristics of Salmonella
- Gram (-) rods
- Motile
- Oxidase and urease negative
- H2S
- Thousands of serovars
- Acquired from contaminated food
Typical size of infectious dose for Salmonella?
Large dose (compared to small dose in Shigella)
Describe pathogenesis of Salmonella
- 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
What are the virulence factors of Salmonella?
- Ipf - enhances adhesion to M cell
- T3SS
- SipB - macro apoptosis
What are additional virulence factors for S. typhi?
- Spi Type 3 - remodels phagosomes for systemic spread
- Vi antigen - capsule for immune evasion
What is the risk of HUS for Salmonella infection?
There is no riskk
What is the general mechanism for typhoid fever?
- Salmonella (typhi or paratyphi) invade M cells
- Disseminat thru macros
- Once critical density reached, macros apoptose and escape into bloodstream
In what organ does salmonella sequester?
Gallbladder
What allele is protective against penetration of the gut?
CFTR cystic fibrosis allele (possibly why the gene has not disappeared from the gene pool)
What is a sign on physical exam of typhoid fever?
Rose spots
RFs for typhoid fever?
- Corticosteroids
- Immunosuppresion
- Malignancy
- Diabetes
PE signs of Salmonella Enterocolitis?
- Nonbloody diarrhea, fever, dehydration
In addition to Tx, what should one do once salmonella has been Dx?
Inform local health authorities!
What are tipoffs of typhoid fever?
Traveling abroad; Rose spots
Tx for salmonella enteric fevers/septicemia?
Ceftriaxone/ciprofloxacin
