Vibrio cholerae El Tor biotype caused the 7th pandemic of cholera. Compared to the classical biotype, El Tor biotype has which property that contributes to its pandemic fitness?
- A El Tor produces a more potent cholera toxin (CT) causing higher fluid loss
- B El Tor exclusively infects children under 5 years
- C El Tor expresses different O-antigen (O139) that vaccinates do not cover
- D El Tor is resistant to polymyxin B and produces haemolysin, and has greater environmental survival and asymptomatic carriage ✓
Explanation
V. cholerae El Tor biotype has several features that make it more pandemic-fit than classical biotype: it is resistant to polymyxin B (used for biotyping), produces El Tor haemolysin (Kanagawa phenomenon on Wagatsuma agar), survives better in environmental water sources (biofilm formation), causes more asymptomatic or mild infections (higher ratio of inapparent to symptomatic infections ~1:10 to 1:100 vs 1:2 for classical), and thus has a larger transmission reservoir. Classical biotype produces slightly more CT and causes more severe cholera per symptomatic case. O139 is a separate serogroup (Bengal), not a biotype property. Both biotypes are O1.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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