Exam #5: Bacterial Infections of the GI Tract II Flashcards
What does MacConkey agar test? What does a positive test look like & what bacteria are associated with it? What does a negative test look like, and what bacteria are associated with it?
MacConkey agar= lactose fermentation
Positive= red colonies/ agar
- E. coli
Negative= white colonies/ agar
- Salmonella, Shigella
What is the Indole test? What does a positive test look like & what bacteria are associated with it? What does a negative test look like, and what bacteria are associated with it?
A test for indole production
Positive= red
- E. coli
- Virbri
Negative= white
- Salmonella
What does a positive Hydrogen Sulfite (H2S) production test look like ? What is it indicative of?
A positive test shows as a black precipitate. It is used to differentiate between Salmonella & Shigella.
- Salmonella= black (producer)
- Shigella= white (non-producer)
List the different virotypes of pathogenic E. Coli & their acronyms.
Enterotoxigenic (ETEC)
Enteropathogenic (EPEC)
Enterohemorrhagic (EHEC)
Enteroinvasive (EtEC)
Describe the characteristics of EPEC.
Gram (-) rod Lactose fermenter Fast Lactose fermenter Facultative anaerobe Moderately invasive
What is EPEC associated with?
Pediatric diarrhea
*Note that specifically, EPEC is associated with pediatric watery diarrhea, which is caused by tissue destruction.
Think P for Peds
Describe the mechanism of action of EPEC.
1) BfpA (bundle forming pilus) binds the the intestinal epithelium
2) Type III Secretion System
What are the clinical manifestations of EPEC?
Watery diarrhea without toxins
What are the morphological characteristics of EPEC?
Attaching & effacing
How is EPEC diagnosed?
Culture & biochemical tests
- Ferments lactose, thus it is red on MacConkey agar
- Indole positive i.e. red on indole test
PCR
What is the treatment for EPEC?
Supportive therapy
Antibiotics can reduce the length of disease, but not routinely used
What are the characteristics of ETEC?
Gram negative rod Lactose fermenter Fast lactose fermenter Faculative anaerobe NOT invasive
What is ETEC assocaited with?
“Traveler’s diarrhea”
Associated with travel to developing countries and consumption of contaminated water or ice (produces a watery diarrhea)
Describe the mechanism of action of ETEC.
1) Fimbraie adhere to the epithelial cell wall
2) Toxins are produced:
- LT
- ST
What is the difference between LT & ST toxins?
LT= AB toxin that increases adenylate cyclase & cAMP, increasing the production of solutes that produce osmotic effect–>diarrhea
ST= Non- AB toxin that increases cGMP and solute movement that osmotically produces watery diarrhea
How is ETEC diagnosed?
- Clinically
- DNA probes to detect LT & ST
How is ETEC treated?
Supportive therapy
Describe the characteristics of Salmonella Typhi.
Gram negative rod Lactose non-fermenter Oxidase negative Facultative anaerobe Motile Flagellated (+ H-antigen) Acid tolerant
How is Salmonella typhi transmitted?
Human to human
Fecal to oral
What are the clinical manifestations of Salmonella typhi?
- Fever with headache
- Rising fever over 3 days
- Thyphoid fever
- GI symptoms
Note that there is a 13 day incubation period
Describe the mechanism of action of Salmonella typhi.
1) Adherence to M-cells (antigen presenting cells to the Peyer’s patch in the ileum) & enterocytes
2) Type III secretion system, secretes SSPs into the cell that causes membrane ruffling & escape from the vacuole
3) Escape from the cytosol
4) Can then travel to the lymph or bloodstream, causing bacteremia/ spesis
How is Salmonella typhi diagnosed?
Culture of stool and blood samples on selective media
How is Salmonella typhi treated?
Antibiotic therapy based on susceptibility profile
How is Salmonella typhi prevented?
Avoid potential sources of infection
- Drink bottled water (no ice)
- Eat thoroughly cooked food
- Avoid raw fruits & vegetables
Vaccination for travelers to endemic areas
