Vibrio cholerae Classical Biotype Strains Reveal Distinct Signatures in

Vibrio choleraeO1 classical (CL) biotype caused the fifth and sixth pandemics, and probably the earlier cholera pandemics, be-fore the El Tor (ET) biotype initiated the seventh pandemic in Asia in the 1970s by completely displacing the CL biotype. Al-though the CL biotype was thought to be extinct in Asia and although it had never been reported from Latin America, V. chol-erae CL and ET biotypes, including a hybrid ET, were found associated with areas of cholera endemicity inMexico between 1991 and 1997. In this study, CL biotype strains isolated from areas of cholera endemicity inMexico between 1983 and 1997 were characterized in terms of major phenotypic and genetic traits and compared with CL biotype strains isolated in Bangladesh be-tween 1962 and 1989. According to sero- and biotyping data, all V. cholerae strains tested had the major phenotypic and geno-typic characteristics specific for the CL biotype. Antibiograms revealed the majority of the Bangladeshi strains to be resistant to trimethoprim-sulfamethoxazole, furazolidone, ampicillin, and gentamicin, 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 of the CL biotype strains although theMexican strains differed from the Bangladeshi strains in 1 to 2 DNA bands. The difference was subtle but consistent, as confirmed by the subclusterin