Enterobacteriaceae Overt Pathogens Flashcards
Slightly selective enteric agar:
- MAC; ID of LF’s
- Eosin Methylene Blue; ID of NLF-weak LF-strong LF
Moderately selective agar:
- XLD
- HE
- SS
Name 3 enrichment media for Salmonella/Shigella:
- Selenite broth
- Tetrathionate broth
- GN (gram neg) broth
What are the 3 categories of infection for Salmonella spp.?
- Gastroenteritis and diarrhea
- Bacteremia and extraintestinal infection
- Enteric fever (typhoid)
Describe pathogenesis: Salmonella spp.
- Capsule protects from stomach acid
- Attachment and phagocytosis by intestinal mucosal cells
- Survive in/destroy phagocytes
- Dissemination to other tissues
Name the Salmonella enterica serotypes.
- “O” Antigen-somatic, body
- “H” Antigen
- “K” Antigen
Describe “O” antigen
- Lipopolysaccharide in outer membrane of cell wall
- Heat stable
- Tube/slide agglutination
Describe “H” antigen
- Flagellar protein
- Heat labile (inactivated at >60o C
- Tube/slide agglutination
Describe “K” antigen
- Polysaccharide envelope antigens (capsular)
- Heat labile
- S. Serotype Typhi produces unique “Vi” antigen that masks other “O” antigens during testing (Remove by boiling for 30 min)
How do you presumptively ID Salmonella spp. in the lab on plates.
- BA: grey, large, smooth
- MAC: NLF
- XLD: Red w/ black center
- HE: Green w/ black precip
- SS: Colorless w/ black center
- Glucose pos
Name significant biochemical tests for the ID of Salmonella spp.
- Oxidase: neg
- TSI: K/A +/- gas, H2S pos
- Motility: pos
- Lysine: pos
- Citrate: pos
- Indole: neg
- Ornithine: most pos
Describe multidrug-resistant typhoid fever (MDRTF)
- In S. serotype Typhi strains
- Resistant to chloramphenicol, ampicillin and cotrimoxazole
- AMS: No single test detects quinolone resistance mech’s
- Test MIC of ciprofloxacin, levofloxacin and/or ofloxacin
How is Shigella spp. transmitted?
- Not NF in humans
- Person to person, via fecal-oral
- Small infective dose
Virulence factors of Shigella spp.
- Mediate adherence and invasion of mucosal cells
- Escape from phagocytic vesicles
- Intercellular spread invasion
- SHIGA toxin (cytotoxin)
Shigella spp. can cause what?
- Bacillary dysentery (shigellosis): Acute inflammatory colitis and blody diarrhea
Presumptive ID of Shigella on plates
- BA: Grey, large, smooth, S.sonnei has jagged edges
- MAC: NLF
- XLD: Colorless (red)
- HE: Green/blue green
- SS: Colorless
What biochemical tests are used to ID Shigella spp.?
- Oxidase: neg
- TSI: K/A
- Lysine: neg
- Motility: neg
- Citrate: neg
- Malonate: neg
- Urea: neg
- ONPG: neg (except S.sonnei
What test distinguishes Shigella spp. from E.coli?
- Lysine
Shigella = neg
E. coli = pos - Acetate utilization
Shigella = neg
E. coli = pos
Name the 4 antisera groups for Shigella spp. based on “O” antigen
- Group A: S. dysenteriae
- Group B: S. flexneri
- Group C: S. boydii
- Group D: S. sonnei
Characteristics of E. coli 0157:H7
- Most common EHEC
- NF in GIT of cattle
Virulence:
- Attachment, cytotoxin (SHIGA-like)
What plate is used to isolate E. coli 0157:H7?
Sorbitol MacConkey (MAC-SOR, SMAC or SORB_
- Lactose replaced by sorbitol
- Crystal violet and bile salts
- NSF (non-sorbitol fermenter; colorless)
Presumptive ID E. coli 0157:H7 on culture plates.
- BA: grey, large, smooth, may be β-hemolytic
- MAC: LF or NLF
- XLD: yellow (if it grows)
- SMAC: NSF
- TSI: Most A/A w/ gas (some K/A w/g)
- MIL: all pos
- Serotype NSF’s w/ latex agglutination (Somatic antigen:0157; Flagellar antigen:H7)
Characteristics and virulence of Yersinia spp.
- Not NF in humans
- Transmitted: Under-cooked food, dairy, contaminated water, contact w/ infected animals
- Virulence: attach and invade intestinal mucosa
Selective agar for Yersinia spp.:
CIN
- Yersinia spp: MF. Tiny/small at 24hrs
- Aeromonas spp: MF
