Molecular epidemiological studies of Vibrio cholerae in Taiwan: genotyping by polymerase chain reaction and DNA sequencing.

To type the Vibrio cholerae strains isolated from sporadic and epidemic cases in Taiwan, 28 toxigenic isolates were studied by sequencing polymerase chain reaction-amplified cholera toxin gene (ctx) fragments. Based on specific base substitutions on positions 115 and 203 of ctxB and comparison with previously published typing system from Centers for Disease Control and Prevention (Olsvik theta et al., J Clin Microbiol 1993; 31:22-5, Ref.1), two genotypes were identified. Cholera strains from imported seafood and sporadic cases in Taiwan had ctxB polymorphism of genotype 1; strains from patients in the 1962 Taiwan epidemic and Taiwan raised soft-shell turtles had ctxB polymorphism of genotype 3. Moreover, one toxigenic non-O1 strain was found to have other 11 different nucleotides in ctxB compared with those of the O1 and O139 strains. Therefore, DNA sequencing is a useful method for obtaining more complete genetic information. The approach could be improved by applying it to other more polymorphic regions of bacterial genome to obtain better epidemiological information among infected cases.