Detection of cholera (ctx) and zonula occludens (zot) toxin genes in Vibrio cholerae O1, O139 and non-O1 strains.

Vibrio cholerae O1 and V. cholerae non-O1 strains isolated from environmental samples collected in São Paulo, Brazil, during cholera epidemics and pre-epidemic periods were examined for the presence of toxin genes. V. cholerae O1 strains isolated from clinical samples in Peru and Mexico, and V. cholerae O139 strains from India were also examined for the presence of ctx (cholera toxin gene) and zot (zonula occludens toxin gene) by polymerase chain reaction (PCR). A modified DNA-extraction method applied in this study yielded satisfactory recovery of genomic DNA from vibrios. Results showed that strains of V. cholerae O1 isolated during the preepidemic period were ctx (-)/zot (-) whereas strains isolated during the epidemic were ctx (+)/zot (+). All V. cholerae non-O1 strains tested in the study were ctx (-)/zot (-), whereas all V. cholerae O139 strains were ctx (+)/zot (+). Rapid detection of the virulence genes (ctx and zot) can be achieved by PCR and this can serve as an important tool in the epidemiology and surveillance of V. cholerae.