Exam #5: Bacterial Infections of the GI Tract III Flashcards
List the characteristics of Vibrio cholerae.
Gram negative "comma-shaped" Grows in alkaline media Facultative anaerobe Flagellated Free-living in water Wide temperature range for growth Require NaCl for growth Susceptible to stomach acid; thus, require a high infectious dose
What diseases does Vibrio cholerae cause?
Gastroenteritis
Bacteremia
(Cholera)
What diseases does Vibrio parahaemolyticus cause?
Gastroenteritis
Bacteremia
Wound infections
What are the symptoms of Cholera?
Wide range of clinical manifestations, from asymptomatic to
severe (lethal) watery diarrhea that can kill within hours
- Abrupt onset
- “rice water stool” (mucous)
What is Vibrio cholerae associated with?
Spread through contaminated water
*Remember “broad street pump” London
Does Vibrio cholerae infection lead to long-term immunity? Why or why not?
Generally, yes
- Immunity is O-antigen specific (LPS antigen)
- IF there is a different strain of O-antigen, then one will NOT be immune
What antigen is associated with Vibrio cholerae?
O-antigen (LPS)
- Specifically, O1 is the cholera toxin producing strain
- There are been 7x pandemics
- 1-6 were caused by classic O1
- Currently we are in #7, “El tor” associated (less severe, but longer carriage time)
Non-O1 do NOT produce cholera toxin
What virulence factors are associated with Vibrio cholerae?
1) Toxin co-regulated pilus (TCP, co-regulated with cholera toxin), which mediates Vibrio cholerae adherence in intestinal epithelial cells (& then cholera toxin is produced)
2) Cholera toxin, which is an AB toxin that activates adenylate cyclase & leads to an increase in cAMP/ massive efflux of watery secretions
- No cell damage
- Similar to ETEC LT toxin
- Encoded on prophage
How is Vibrio cholerae infection diagnosed?
Culture on differential media
How is Vibrio cholerae infection treated?
Rehydration therapy (IV)
What are the symptoms caused by Vibrio parahaemolyticus?
Explosive watery diarrhea Nausea Vomiting Abdominal cramps Low grade fever
What is the virulence factor associated with Vibrio parahaemolyticus?
Kanagawa hemolysin, which induces Cl- secretion & thus, watery diarrhea
What is Vibrio parahaemolyticus associated with?How is Vibrio parahaemolyticus prevented?
- Seafood-associated gastroenteritis (most common is Gulf states in US)
- Proper cooking of shellfish
How is Vibrio parahaemolyticus treated?
Self-limiting
Supportive therapy
What are the characteristics of Yersinia enterocolitica?
Gram negative coccobacilli
What is Yersinia enterocolitica associated with?
Improperly cooked pork
What are the symptoms of Yersinia enterocolitica infection?
Fever
Abdominal cramps
Watery to bloody diarrhea
Describe the mechanism of action of Yersinia enterocolitica infection.
- Binds to & invades M-cells in the terminal ileum (similar to Salmonella)
- Involves T3SS and injection of Yops (Yersinia outer proteins)
- Produces a heat-stable enterotoxin
How is Yersinia enterocolitica diagnosed?
Stool culture
How is Yersinia enterocolitica treated?
Self-limiting
Supportive therapy
What are the organisms associated with the large intestine?
C. diff
What are the characteristics of Clostridium difficile?
Gram-positive rod
Anaerobic Test positive
Non-invasive
Spore-forming
Emerging nosocomial infection
What are the symptoms of Clostridium difficile infection?
Disease & symptoms vary
- Asymptomatic
- CDAD
- Pseudomembrane colitis
- Fulminant colitis
- Toxic megacolon
What are the symptoms of CDAD?
Clostridium difficile associated diarrhea
- watery diarrhea
- fecal leukocytes
- occult blood sometimes seen
What are the symptoms of Pseudomembrane colitis?
- C. diff forms large plaques on intestinal epithelium, limiting water uptake
- As this grows, toxins can be produced, which leads to fulminant colitis
- Symptoms:
profuse watery diarrhea
fecal luekocyutes
occult blood sometimes seen
What are the symptoms of fulminant colitis?
Necrosis of the large intestine from C. diff toxin
- diarrhea may be severe or diminished
- surgical consult required; patient may present with acute abdomen
What are the major virulence factors of Clostridium difficile?
Toxin A
Toxin B
Both cause damage to the mucosa; disruption of the host cell cytoskeleton leads to diarrhea
How is Clostridium difficile diagnosed?
Toxin detection in stool
Culture NOT helpful
*Note that this is commonly seen in patients that are on broad spectrum antibiotics in the hospital
How is Clostridium difficile treated?
Oral vancomycin or metronidazole
How is Clostridium difficile prevented?
Fecal transplant
What are the characteristics of EHEC?
Enterohemorrhagic E. Coli
What is EHEC associated with?
Contaminated ground beef & vegetables
What disease is caused by EHEC?
Hemorrhagic colitis i.e. FRANK bloody diarrhea. Symptoms:
- NO fever
- marked abdominal tenderness
What sequelae is associated with EHEC?
Hemolytic Uremic Syndrome (HUS) that can lead to anemia and renal failure
Describe the mechanism of action of EHEC.
- EHEC binds & attaches to enterocytes, causing an attaching & effacing lesion like EPEC
- Also, produces Shiga-like toxin (verotoxin), which blocks translation by cleaving part of the 60S ribosome, which has the effect of destroying cell/ microvilli
- Verotoxin can enter blood, causing vascular endothelial damage & increased platelet aggregation
- Platelet-fibrin thrombi form causing ischemic damage to colon, kidneys, and other tissues, leading to hemorrhagic colitis
- Also, the kidney is rich in the toxin glycolipid receptor (Gb3)–binding to verotoxin leads Hemolytic uremic syndrome & renal failure
Note that cattle & other ruminants LACK Gb3, which is why they can be a reservoir
How is EHEC diagnosed?
- Clinically presumptive: bloody diarrhea WITHOUT fever
- Culture: MacConkey’s agar (lactose fermentation)
- PCR (NAAT) to detect Shiga-toxin gene
How is EHEC treated?
Supportive therapy
Antibiotics are CONTRAINDICATED
- Abx induce damage to the bacterial cell; however, the shiga toxin is encoded on a bacteriophage
- When the bacteriophage detects damage, it lysis the cell and leads to increased release of Shiga-toxin (more HUS)
How is EHEC prevented?
Properly cooked hamburger (& raw vegetables)
What are the characteristics of Shigella?
Gram negative rods Lactose fermenter Oxidase negative Facultative anaerobe Intracellular pathogen
What does Shigella cause?
Dysentery
What is Shigella associated with?
Poor sanitary infrastructure
Crowded healthcare systems
Day care centers
Describe the species distribution of Shigella.
S. soneii= developed countries
S. flexneri= developing countries
S. dysentariae= underdeveloped tropical areas
Describe the clinical manifestation of Shigella.
S. soneii=
- fever
- malaise
- watery diarrhea
S. flexneri & S. dysentariae=
- fever
- malaise
- watery diarrhea
- abdominal cramps
- tensemus (urge to defecate)
- frequently blood & pus-filled stool
Note that S. dysentarie has the potential to develop HUS
Describe the pathogenesis of Shigella.
- Acid resistant
- Adheres selectively to M-cells & invades macrophages
- Rapid escape from phagosome
- Rapid induction of macrophage apoptosis
- Salmonella- like
Also,
- Interacts with the baso-lateral face of enterocytes
- Induces uptake via T3SS
- Lysis of endocytic vacuole
- Spread by actin polymerization at a pole
- Listernia monocytogenes-like
How is Shigella diagnosed?
- Stool culture using selective media
- Serological tests to confirm species
How is Shigella treated?
Rehydration therapy
Antibiotic treatment
What are the characteristics of EIEC?
- Very uncommon
What is the mechanism of action of EIEC?
Same as Shigella with NO Shiga-toxin
Why is EIEC mechanistically related to Shigella?
Appears E. coli obtained pathogenicity island from Shigella via horizontal gene transfer
What is an additional consideration of the fecal-oral route aside from food & fingers?
Anal sex–>mouth
