DISTRIBUTION OF GENES ENCODING CHOLERA-TOXIN, ZONULA OCCLUDENS TOXIN, ACCESSORY CHOLERA-TOXIN, AND EL-TOR HEMOLYSIN IN VIBRIO-CHOLERAE OF DIVERSE ORIGINS

A large collection of 1154 strains of Vibrio cholerae of diverse origins including serogroups 01 and 0139 and those belonging to the non-01 and non-0139 (non-01:non-0139) serogroups were examined with a battery of DNA probes specific for cholera toxin (CT), zonula occludens toxin (ZOT), accessory cholera toxin (ACE) and El Tor hemolysin (HLY) to determine the distribution of genes among wild strains and to understand the importance of these factors in the pathogenesis of the disease cholera. Among the 01 clinical isolates, the majority of the strains had an intact core region (ctx, zot, ace) and also possessed the hlyA gene. Although rare, strains of 01 with natural deletions of the ctx, zot and/or ace genes were also detected. The absence of the virulence genes comprising the core region and the presence of the hlyA gene dominated the 01 environment, food isolates and the clinical and environmental non-01:non-0139 strains of V. cholerae. All the 0139 strains examined in this study possessed genes located in the core region and the hlyA gene. Among all the virulence-associated genes examined, the hlyA gene was the most conserved genetic element in V. cholerae independent of biotypes and serogroups.