Vibrio Cholerae Classical Biotype Strains Reveal Distinct Signatures in Mexico

Vibrio cholerae O1 Classical (CL) biotype caused the 5th and 6th, and probably the earlier cholera pandemics, before the El Tor (ET) biotype initiated the 7th pandemic in Asia in the 1970's by completely displacing the CL biotype. Although the CL biotype was thought to be extinct in Asia, and it had never been reported from Latin America, V. cholerae CL and ET biotypes, including hybrid ET were found associated with endemic cholera in Mexico between 1991 and 1997. In this study, CL biotype strains isolated from endemic cholera in Mexico, between 1983 and 1997 were characterized in terms of major phenotypic and genetic traits, and compared with CL biotype strains isolated in Bangladesh between 1962 and 1989. According to sero- and bio-typing data, all V. cholerae strains tested had the major phenotypic and genotypic characteristics specific for the CL biotype. Antibiograms revealed the majority of the Bangladeshi strains to be resistant to trimethoprim/sulfamethoxazole, furazolidone, ampicillin, and gentamycin, while the Mexican strains were sensitive to all of these drugs, as well as to ciprofloxacin, erythromycin, and tetracycline. Pulsed-field gel electrophoresis (PFGE) of NotI-digested genomic DNA revealed characteristic banding patterns for all the CL biotype strains, although the Mexican strains differed with the Bangladeshi strains in 1-2 DNA bands. The difference may be subtle, but consistent, as confirmed by the sub-clustering patterns in the PFGE-based dendrogram, and can serve as regional signature, suggesting pre-1991 existence and evolution of the CL biotype strains in the Americas, independent from that of Asia.