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Flashcards in E. Coli Deck (67)
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1

E. Coli, Salmonella, Shigella, and other Opportunistic Enterobacteriaceae are all what type of bacterium?

Gram negative facultative anaerobic rods so they ferment glucose, they are oxidase negative, and reduce nitrates to nitrite (dipstick test!)

2

What antigenic structures are used in serotyping E. Coli, Salmonella, Shigella, and other Opportunistic Enterobacteriaceae?

K (capsular) antigens: capsular polysaccharide (Klebsiella)
H (flagellar) antigens
O antigens: O-side of LPS chains

3

How are E. Coli, Salmonella, Shigella, and other Opportunistic Enterobacteriaceae cultured and identified?

Fecal samples on MacConkey
Normally sterile samples cultured on rich media
ID by biochemical tests or serology

4

On a KIA slant what does it mean if the results are Y/Y?

Lactose fermentation; E. Coli

5

On a KIA slant what does it mean if the results are R/Y?

Glucose fermentation; Shigella

6

On a KIA slant what does it mean if the results are Black?

Hydrogen Sulfide production; Proteus

7

On a KIA slant what does it mean if the results are R/R?

No fermentation; Pseudomonas

8

On a KIA slant what does it mean if the results have a bottom gap?

H2 production; E. Coli

9

What is a big problem for the treatment of E. Coli, Salmonella, Shigella, and other Opportunistic Enterobacteriaceae?

Plasmid-mediated antibiotic resistance, although antibiotics are generally not needed

10

What percentage of infectious diarrhea is caused by viruses?

90

11

If diarrhea persists more than 10-14 days what is it most likely?

A parasite

12

If diarrhea is chronic what should begin to be considered?

HIV; it is a big problem in AIDS patients
Mycobacterium avium intracellulare, CMV

13

What diseases does E. Coli cause?

Diarrhea and dysentery, a variety of opportunistic infections (#1 cause of UTIs) including septicemia and meningitis in neonates

14

Where is E. Coli important (regionally)?

In the US and developing world

15

Why do resident E. Coli flora not cause diarrhea?

They lack PAIs

16

What are the cultural characteristics of E. Coli?

Lac+, ferments glucose with gas (H2), does not produce H2S, motile

17

What are the cultural characteristics of Salmonella?

H2S+, Gas + (except S. typhi) Lac -, Glu +

18

What are the cultural characteristics of Shigella?

H2S-, Gas -, Lac -, Glu +

19

What are the 5 types of E. coli?

Enterotoxigenic (ETEC)
Enteroinvasive (EIEC)
Enterohemorrhagic (EHEC)
Enteropathogenic (EPEC)
Enteroaggregative (EAEC)

20

What is EHEC caused by?

Mostly by O157:H7; Undercooked beef, fruits, unpasteurized juices, lettuce, spinach, sprouts, and human to human

21

What are the symptoms of EHEC?

Little fever, acute onset cramps, watery diarrhea that becomes bloody within 24 hours (noninflamm, no leukocytes); Lasts up to 8 days

22

What is the pathogenesis of EHEC?

Low infectious dose (~100), Shiga toxin (Stx) which is an AB toxin that cleaves 28S RNA of the ribosome where the lysogenic phage is encoded

23

What is the important syndrome that follows in about 2-7% of patients? (EHEC)

HUS; HUS and EHEC is the MCC of pediatric acute renal failure; think young and elderly; also anemia. DONT TREAT with abx because it is exacerbated

24

What is the locus of enterocyte effacement for EHEC?

It is a PAI with a type 3 secretion system, it delivers E. coli receptor to host cell, makes pedestal for attachment, and responsible for the diarrhea

25

How is EHEC diagnosed?

O157:H7 cannot use sorbitol so:
White on Sorbitol MacConkey agar
other STEC and E. coli are red/pink
RADT for Stx in stool

26

Why are Abx CI'd in EHEC?

Believed to stress bacteria leading to increased phage expression of Stx

27

What is ETEC?

Traveler's diarrhea

28

What are the virulence factors for ETEC?

CFA I or II for attachment

29

What are the symptoms of ETEC?

High volume watery diarrhea (but nowhere near as much as cholera)

30

What are the 2 toxins of ETEC process?

Heat labile toxin (LT) lie cholera toxin (same mech too as cholera too!); and Heat stabile toxin (ST); net effect is both lead to hyper secretion of chloride and water