31. Vibrio cholerae. Morphology, biology, biochemical production. Antigenic composition. Sero- and biotypes. Pathogenecity and immunity. Microbiological diagnosis. Specific prophylaxis and therapy.

VIBRIO CHOLERAE

General Characteristics

• Gram-negative, comma-shaped curved rods
• Facultative anaerobes
• Motile with a single polar flagellum
• Oxidase-positive (distinguishes from enteric G-rods)
• Non-spore forming
• Grow well at alkaline pH (8.5–9.5) but are killed by acid

• Ferment sucrose and mannose, not arabinose
• Rapid growth on peptone water, blood agar, and TCBS agar (Thiosulfate Citrate Bile Salts Sucrose agar – shows yellow colonies due to sucrose fermentation)
• Show polymorphic forms (S-shaped, filamentous, coccobacilli) in Pfeiffer stain

Virulence Factors of V. cholerae

Lab Diagnosis

• Specimens: stool, vomit
• Microscopy: Gram-negative curved rods, Pfeiffer stain shows "shooting star motility"
• Culture: Grows rapidly on:
• Peptone water
• Blood agar
• TCBS agar (yellow colonies due to sucrose fermentation)
• Biochemical:
• Indole (+)
• Oxidase (+)
• Serology: Gruber agglutination
• Rapid diagnostic tests available (dipsticks, latex agglutination)

Pathogenesis of Cholera

1. Ingestion of contaminated food/water
2. Survival in stomach depends on pH – more likely with antacids
3. Colonization of small intestine via TCP
4. Cholera toxin production → B subunit binds GM1 ganglioside → A subunit activates adenylate cyclase → ↑cAMP → massive secretion of water & electrolytes
5. Results in: profuse watery diarrhea (“rice water stool”), severe dehydration

Clinical Features

• Cholera (O1/O139):
• Sudden onset of profuse watery diarrhea
• Vomiting, dehydration
• Muscle cramps, metabolic acidosis, hypokalemia
• No fever typically
• Milder gastroenteritis with non-O1/non-O139 strains

Treatment

• Primary: Prompt rehydration therapy (oral or IV)
• Antibiotics shorten duration:
• Tetracycline, doxycycline
• Alternative: azithromycin or ciprofloxacin

Prevention

• Clean water supply, sanitation
• Killed or oral cholera vaccine (Dukoral, Shanchol)
• Public health measures during outbreaks