Comparative analysis of factors promoting optimal production of cholera toxin by Vibrio cholerae O1 (classical & E1Tor biotypes) & O139

Abstract

Various culture media [AKI, Brain heart infusion broth (BHI), Casamino acid-yeast extract broth (CAYE), Casamino acid-yeast extract broth supplemented with 90 micrograms/ml of lincomycin (CAYE-L), Tryptic soy broth (TSB) and Yeast extract peptone (YEP)], cultural conditions (stationary and shaking) and incubation temperatures (30 degrees C and 37 degrees C) were evaluated to determine optimal conditions for production of cholera toxin (CT) by different biotypes (classical and E1Tor) and serogroups (O1 and O139) of V. cholerae. It was found that V. cholerae O1 E1Tor grown in CAYE-L and incubated at 30 degrees C with constant shaking was optimal for production of CT, while for the classical biotype and for the O139 serogroup, CT was maximally produced when grown in YEP and incubated at 30 degrees C in a shaker. Temperature appeared to be a prominent factor affecting the production of CT by the O1 E1Tor biotype when the media used were AKI, CAYE-L and YEP and also for the classical biotype when the media used were the AKI, BHI, CAYE and YEP. In the case of the O1 E1Tor biotype, CAYE-L was the best medium for CT production whereas for the classical biotype, CAYE-L was a poor medium as far as CT production was concerned. Irrespective of the media used, 30 degrees C shake culture condition seemed to be more favourable for supporting CT production except in CAYE medium for the O1 E1Tor biotype where incubation at 37 degrees C in a shaker was as good as incubation at 30 degrees C.