Enterobacteriaceae I Flashcards
All of the Enterobacteriaceae appear as _____ on gram staining?
Gram negative rods
What component of the Enterobacteriaceae contributes to septic shock?
LPS
T/F Enterobacteriaceae are obligate anaerobes
FALSE Enterobacteriaceae are facultative anaerobes
When grown anaerobcally, enterobacteriaceae ferment _____
Glucose
What test distinguishes enterobacteriaceae from Pseudomonas?
Oxidase test Reagent remains colorless with enterobacteriaceae, turns colors with pseudomonas
What three surface antigens are used for typing of Enterobacteriaceae?
- 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
*
In septic shock caused by Enterobacteriaceae, bacterial LPS binds _____, causing generation of pro-inflammatory cytokines
CD14 of macrophages
T/F The presence of 20+ PMN per HPF implies the patient has an inflammatory diarrhea (Shigella)
TRUE
Few or no fecal leukocytes is seen in watery diarrheas (toxigenic cholera/viral)
On blood agar, Enterobacteriaceae appear as _____
Gray, mucoid colonies
What are the three treatment options for Traveler’s Diarrhea?
- 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.
Many of the Enterobacteriaceae ferment _____
Lactose
What special agar is used to culture E. coli? How does it look.
- MacConkey’s agar
- Looks cherry pink
- Due to fermentation of lactose, changing pH
E. coli hydrolyzes tryptophan to _____
Indole (positive indole test)
On Eosin Methylene Blue (EMB), E. coli makes acid and creates a _____
Green sheen
Enterotoxigenic E. Coli (ETEC) is transmitted ______, and commonly causes _____.
- Fecal oral transmission
- Commonly causes Traveler’s diarrhea
T/F ETEC invades epithelial cells
FALSE
ETEC only adheres to small intestine via its pili (colonization factor antigens - CFA1 & CFA2)
ETEC stimulates _____ and _____ causing hypersecretion of electrolytes
- Guanylate and adenylate cyclase
What are the two toxins secreted by ETEC?
- Heat stable toxin (ST)
- Heat labile toxin (LT)
- Like cholera toxin, but less potent
_____ E. coli starts off with a watery diarry that eventually becomes bloody and watery
Enteroinvasive E. coli (EIEC)
Treatment for EIEC?
Same as ETEC (Fluoroquinolone, Rifaximin, azithromycin)
What are the symptoms of EIEC?
- Fever
- Cramps
- Malaise
- Toxemia
What is the main reservoir of EHEC?
Cattle
EHEC makes _____ toxin. What does it do?
- 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
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?
- Hemolytic Uremic Sydrome
- Usually affects older folks and kids
- Tx: Transfusions and dialysis
What test can select for EHEC as opposed to other types of E. coli? What specific serotype does this test look for?
- SMAC plating
- Contains sorbitol which EHEC CANNOT ferment
- Will NOT turn color (other E. Coli will)
- Serotype O157:H7 colonies
T/F EHEC should ideally be treated with abx
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)
EAST toxin made by Enteroaggregetic E. Coli (EAggEC) causes _____
Swelling and RBC agglutination
EAggEC symptoms? Tx?
- Persistent watery diarrhea
- May be mistaken for norovirus
- Tx: Same as ETEC and EIEC
- Rifaximin, azithromycin, fluoroquinoloes
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.
Type III Secretion
