Vibrio cholerae O1 El Tor biotype is isolated from a cholera outbreak. Which set of laboratory tests best confirms this biotype designation compared to the Classical biotype?
- A El Tor biotype: VP negative, haemolysin negative, sensitive to polymyxin B, resistant to Mukerjee phage group IV
- B El Tor biotype: Voges-Proskauer (VP) positive, haemolysin positive (El Tor haemolysin), resistant to polymyxin B (50 units disc), sensitive to Group IV phage ✓
- C El Tor biotype: Cholera red reaction positive, string test negative, resistant to vibriostatic agent O/129
- D El Tor biotype: Oxidase positive, grows on TCBS (yellow colony), resistant to bile salt agar distinguishing it from Classical biotype
Explanation
V. cholerae O1 El Tor biotype is distinguished from the Classical biotype by: (1) VP (Voges-Proskauer) test positive — El Tor ferments glucose to 2,3-butanediol; Classical is VP-negative; (2) Production of El Tor haemolysin (beta-haemolysin on sheep blood agar); Classical is non-haemolytic; (3) Resistance to polymyxin B (50 unit disc) — Classical is sensitive; (4) Resistance to Mukerjee's phage group IV — Classical is sensitive; (5) Agglutination of chicken RBCs (haemagglutinin). Both biotypes are oxidase-positive and grow on TCBS as yellow colonies (sucrose fermenters). The vibriostatic agent O/129 sensitivity is the same for both biotypes.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.