Vibrio cholerae

1. Morphology and Identification

• Comma-shaped, curved rod with a polar flagellum
• Oxidase-positive
• Rapidly killed by acid & grow at a very high pH (8.5-9.5)
• Halotolerant or halophilic : grows on media containing 6% NaCl

2. Antigenic Structure

• A single heat-labile flagella H antigen
• O lipopolysaccharides : serologic specificity
• V cholerae serogroups O1 and O139; classic cholera (Table 18-1)
• V cholerae serogroups non-O1 and non-O139 ; Cholera-like diarrhea

3. Vibrio cholerae Enterotoxin

Produce a heat-labile enterotoxin (Subunits A and B); chromosomal control (the same mechnism of action as E.coli's LT toxin, but LT is transmitted via s plasmid)

binding to Ganglioside GM1 on intestinal epithelium by subunit B ≫ entry of the A subunit ≫ Subunit A activate G-protein ≫ stimulate the activity of a membrane-bound adenylate cyclase ≫ production intracellular cAMP ≫ secretion of Na and Cl and inhibition of Na and Cl reabsorption ≫ prolonged hypersecretion of water and electrolytes ≫ diarrhea (20-30 L/d) ≫ dehydration

4. Pathogenesis & Clinical Findings

• Infective dose: 108-1010 organisms
• Not an invasive infection
• About 60% of infection with classic V Cholerae: Asymptomatic
• Incubation period (1-4 days) ≫ Sudden onset of nausea and vomiting, profuse diarrhea with abdominal cramps, rice-water like stool (mucus, epithelial cells, large numbers of vibrios) ≫ profound dehydration, circulatory collapse and anuria, mortality rate without treatment is 25-50%

5. Immunity ; Partial immunity to reinfection

• some protection by gastric acid

6. Treatment

• Water and electrolyte replacement & oral tetracycline.

7. Epidemiology, Prevention & Control

• Endemic in India and Southeast Asia
• Spread by person-to-person and by water, food, and flies.
• Control: education and improvement of sanitation, particularly of food and water
• Chemoprophylaxis, and repeated injection of a vaccine: limited protection to heavily exposed persons

Category: Microbiology Notes