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Carbohyrdrates and Microbiology :) > Enterobacteriaceae Overt Pathogens > Flashcards

Enterobacteriaceae Overt Pathogens Flashcards

1
Q

Slightly selective enteric agar:

A
  • MAC; ID of LF’s

- Eosin Methylene Blue; ID of NLF-weak LF-strong LF

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2
Q

Moderately selective agar:

A
  • XLD
  • HE
  • SS
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3
Q

Name 3 enrichment media for Salmonella/Shigella:

A
  • Selenite broth
  • Tetrathionate broth
  • GN (gram neg) broth
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4
Q

What are the 3 categories of infection for Salmonella spp.?

A
  • Gastroenteritis and diarrhea
  • Bacteremia and extraintestinal infection
  • Enteric fever (typhoid)
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5
Q

Describe pathogenesis: Salmonella spp.

A
  • Capsule protects from stomach acid
  • Attachment and phagocytosis by intestinal mucosal cells
  • Survive in/destroy phagocytes
  • Dissemination to other tissues
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6
Q

Name the Salmonella enterica serotypes.

A
  • “O” Antigen-somatic, body
  • “H” Antigen
  • “K” Antigen
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7
Q

Describe “O” antigen

A
  • Lipopolysaccharide in outer membrane of cell wall
  • Heat stable
  • Tube/slide agglutination
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8
Q

Describe “H” antigen

A
  • Flagellar protein
  • Heat labile (inactivated at >60o C
  • Tube/slide agglutination
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9
Q

Describe “K” antigen

A
  • 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)
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10
Q

How do you presumptively ID Salmonella spp. in the lab on plates.

A
  • BA: grey, large, smooth
  • MAC: NLF
  • XLD: Red w/ black center
  • HE: Green w/ black precip
  • SS: Colorless w/ black center
  • Glucose pos
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11
Q

Name significant biochemical tests for the ID of Salmonella spp.

A
  • Oxidase: neg
  • TSI: K/A +/- gas, H2S pos
  • Motility: pos
  • Lysine: pos
  • Citrate: pos
  • Indole: neg
  • Ornithine: most pos
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12
Q

Describe multidrug-resistant typhoid fever (MDRTF)

A
  • 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
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13
Q

How is Shigella spp. transmitted?

A
  • Not NF in humans
  • Person to person, via fecal-oral
  • Small infective dose
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14
Q

Virulence factors of Shigella spp.

A
  • Mediate adherence and invasion of mucosal cells
  • Escape from phagocytic vesicles
  • Intercellular spread invasion
  • SHIGA toxin (cytotoxin)
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15
Q

Shigella spp. can cause what?

A
  • Bacillary dysentery (shigellosis): Acute inflammatory colitis and blody diarrhea
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16
Q

Presumptive ID of Shigella on plates

A
  • BA: Grey, large, smooth, S.sonnei has jagged edges
  • MAC: NLF
  • XLD: Colorless (red)
  • HE: Green/blue green
  • SS: Colorless
17
Q

What biochemical tests are used to ID Shigella spp.?

A
  • Oxidase: neg
  • TSI: K/A
  • Lysine: neg
  • Motility: neg
  • Citrate: neg
  • Malonate: neg
  • Urea: neg
  • ONPG: neg (except S.sonnei
18
Q

What test distinguishes Shigella spp. from E.coli?

A
  • Lysine
    Shigella = neg
    E. coli = pos
  • Acetate utilization
    Shigella = neg
    E. coli = pos
19
Q

Name the 4 antisera groups for Shigella spp. based on “O” antigen

A
  • Group A: S. dysenteriae
  • Group B: S. flexneri
  • Group C: S. boydii
  • Group D: S. sonnei
20
Q

Characteristics of E. coli 0157:H7

A
  • Most common EHEC
  • NF in GIT of cattle

Virulence:
- Attachment, cytotoxin (SHIGA-like)

21
Q

What plate is used to isolate E. coli 0157:H7?

A

Sorbitol MacConkey (MAC-SOR, SMAC or SORB_

  • Lactose replaced by sorbitol
  • Crystal violet and bile salts
  • NSF (non-sorbitol fermenter; colorless)
22
Q

Presumptive ID E. coli 0157:H7 on culture plates.

A
  • 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)
23
Q

Characteristics and virulence of Yersinia spp.

A
  • Not NF in humans
  • Transmitted: Under-cooked food, dairy, contaminated water, contact w/ infected animals
  • Virulence: attach and invade intestinal mucosa
24
Q

Selective agar for Yersinia spp.:

A

CIN

  • Yersinia spp: MF. Tiny/small at 24hrs
  • Aeromonas spp: MF
25
Q

Presumptive ID of Yersinia enterocolitica on culture plates:

A
  • Grows well at 4-43, “cold enrichment” at 25-30
  • BA: grey, large, smooth
  • MAC: NLF or LLF
  • HE: salmon
  • XLD: yellow/colorless
  • CIN: MF, “bulls eye” at 48hrs
26
Q

Biochemicals used to ID Yersinia enterocolitica in lab

A
  • TSI: A/A
  • Motility: Neg @35, pos @25
  • Lysine: neg
  • Ornithine: pos
  • Indole: v
  • Urea: pos (75%)

Carbohyrdrates and Microbiology :) (7 decks)

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