El Tor biotype of Vibrio cholerae O1 differs from Classical biotype in all of the following EXCEPT:

• A Haemolysin production (El Tor positive, Classical negative in original strains)
• B Voges-Proskauer (VP) test: El Tor positive, Classical negative
• C Production of cholera toxin (CT): El Tor does not produce CT ✓
• D Resistance to polymyxin B: El Tor resistant

Explanation

Both El Tor and Classical biotypes of V. cholerae O1 produce cholera toxin (CT) encoded by the CTX prophage; this is NOT a differentiating feature. El Tor is differentiated by: VP test positivity, haemolysin production (original El Tor strains; some hybrid strains are VP-negative, CT-high producing), resistance to polymyxin B (50 units), and agglutination of chicken RBCs. Altered El Tor variants carrying Classical CT genes now dominate pandemic strains but both produce CT.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.