The El Tor biotype of Vibrio cholerae O1 has undergone genetic changes producing the 'altered El Tor' or 'hybrid El Tor' variant. What is the hallmark of this variant compared to classical El Tor?
- A Produces CT (cholera toxin) of classical biotype, causing more severe watery diarrhoea than typical El Tor ✓
- B Lacks the El Tor haemolysin and therefore cannot be identified by Greig haemolysin test
- C Is resistant to all first-line antibiotics (tetracycline, ampicillin, trimethoprim)
- D Belongs to serogroup O139 and does not produce cholera toxin
Explanation
The 'altered El Tor' (hybrid El Tor) variant produces cholera toxin (CT) encoded by the classical ctxB gene instead of the El Tor ctxB allele. Classical CT is more potent than El Tor CT, explaining the more severe, rice-water diarrhoea seen in outbreaks caused by this variant since the 2000s in Bangladesh, India, and West Africa. This variant retains El Tor biotype characteristics (haemolysis, Polymyxin B resistance profile) but has acquired classical-type toxin genes through horizontal gene transfer. It differs from O139 (Serogroup O139 Bengal emerged in 1992, is non-O1, and does produce cholera toxin — option D is incorrect).
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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