Enterobacteriaceae I

Question 1

All of the Enterobacteriaceae appear as _____ on gram staining?

Answer 1

Gram negative rods

Question 2

What component of the Enterobacteriaceae contributes to septic shock?

Answer 2

LPS

Question 3

T/F Enterobacteriaceae are obligate anaerobes

Answer 3

FALSE Enterobacteriaceae are facultative anaerobes

Question 4

When grown anaerobcally, enterobacteriaceae ferment _____

Answer 4

Glucose

Question 5

What test distinguishes enterobacteriaceae from Pseudomonas?

Answer 5

Oxidase test Reagent remains colorless with enterobacteriaceae, turns colors with pseudomonas

Question 6

What three surface antigens are used for typing of Enterobacteriaceae?

Answer 6

• O (ohne Hauch) antigen
  
  • Repeating unit of carbs on outermost portion of LPS
• H (Hauch) antigen
  
  • Flagellar antigen
• K (Kapsel) antigen
  
  • Capsular, usually polysaccharide
  • Called Vi in Salmonella typhi (due to unique virulence properties
    *

Question 7

In septic shock caused by Enterobacteriaceae, bacterial LPS binds _____, causing generation of pro-inflammatory cytokines

Answer 7

CD14 of macrophages

Question 8

T/F The presence of 20+ PMN per HPF implies the patient has an inflammatory diarrhea (Shigella)

Answer 8

TRUE

Few or no fecal leukocytes is seen in watery diarrheas (toxigenic cholera/viral)

Question 9

On blood agar, Enterobacteriaceae appear as _____

Answer 9

Gray, mucoid colonies

Question 10

What are the three treatment options for Traveler’s Diarrhea?

Answer 10

• Azithromycin
• Cipro
• Rifaximin

Note: these do not cure the condition, but they shorten the duration of symptoms. Thus, fluid and electrolyte replacement is suggested to prevent bacterial resistance.

Question 11

Many of the Enterobacteriaceae ferment _____

Answer 11

Lactose

Question 12

What special agar is used to culture E. coli? How does it look.

Answer 12

• MacConkey’s agar
• Looks cherry pink
  
  • Due to fermentation of lactose, changing pH

Question 13

E. coli hydrolyzes tryptophan to _____

Answer 13

Indole (positive indole test)

Question 14

On Eosin Methylene Blue (EMB), E. coli makes acid and creates a _____

Answer 14

Green sheen

Question 15

Enterotoxigenic E. Coli (ETEC) is transmitted ______, and commonly causes _____.

Answer 15

• Fecal oral transmission
• Commonly causes Traveler’s diarrhea

Question 16

T/F ETEC invades epithelial cells

Answer 16

FALSE

ETEC only adheres to small intestine via its pili (colonization factor antigens - CFA1 & CFA2)

Question 17

ETEC stimulates _____ and _____ causing hypersecretion of electrolytes

Answer 17

• Guanylate and adenylate cyclase

Question 18

What are the two toxins secreted by ETEC?

Answer 18

• Heat stable toxin (ST)
• Heat labile toxin (LT)
  
  • Like cholera toxin, but less potent

Question 19

_____ E. coli starts off with a watery diarry that eventually becomes bloody and watery

Answer 19

Enteroinvasive E. coli (EIEC)

Question 20

Treatment for EIEC?

Answer 20

Same as ETEC (Fluoroquinolone, Rifaximin, azithromycin)

Question 21

What are the symptoms of EIEC?

Answer 21

• Fever
• Cramps
• Malaise
• Toxemia

Question 22

What is the main reservoir of EHEC?

Answer 22

Cattle

Question 23

EHEC makes _____ toxin. What does it do?

Answer 23

• Shiga toxin
  
  • Made by both E. coli and Shigella
  • A-B toxin
  • B subunit binds ganglioside receptor
  • A subunit exits golgi → modifies tRNA binding site of 60S
    
    • Stops protein synthesis → death

Question 24

What occurs when shiga toxin damages blood vessels in the epithelium of glomeruli, with resultant in kidney failure and thrombocytopenia leading to renal failure, neuro. deficits (5-10%), and death (5-10%). What populations does this condition usually effect? How is it treated?

Answer 24

• Hemolytic Uremic Sydrome
  
  • Usually affects older folks and kids
  • Tx: Transfusions and dialysis

Question 25

What test can select for EHEC as opposed to other types of E. coli? What specific serotype does this test look for?

Answer 25

* SMAC plating * Contains sorbitol which EHEC CANNOT ferment * Will NOT turn color (other E. Coli will) * Serotype O157:H7 colonies

Question 26

T/F EHEC should ideally be treated with abx

Answer 26

FALSE Ideally rehydration and electrolytes only, because some abx have been shown to induve toxin synthesis and release or promote HUS. Imodium is also contraindicated (limits perstalsis, preventing flushing of bacteria)

Question 27

EAST toxin made by Enteroaggregetic E. Coli (EAggEC) causes \_\_\_\_\_

Answer 27

Swelling and RBC agglutination

Question 28

EAggEC symptoms? Tx?

Answer 28

* Persistent watery diarrhea * May be mistaken for norovirus * Tx: Same as ETEC and EIEC * Rifaximin, azithromycin, fluoroquinoloes

Question 29

After binding to intestinal cells with bundle forming pili, EPEC uses a type _____ secretion of virulence factor to induce formation of a receptor/pedestal E. coli can bind to.

Answer 29

Type III Secretion