Pathogenic Potential of Non-O1, Non-O139 Vibrio cholerae

Abstract

Vibrio cholerae organisms are known to exist in more than 200 different serogroups based on their “O” antigenic characters. Out of these, strains belonging to O1 or O139 serogroups have been implicated as the causative agent of cholera in the epidemic form. On the other hand, V. cholerae non-O1, non-O139 organisms, ubiquitously present in the aquatic environment, are usually nonpathogenic in nature. However, these strains can be isolated from sporadic cases or occasional outbreaks of gastroenteritis in man. Recently, there has been an upsurge in their isolation rate from diarrheal patients in the cholera endemic areas. Detailed characterization of these strains has demonstrated considerable diversity in their phenotypic as well as genotypic properties that may not be related to their pathogenic potential. While non-O1, non-O139 strains can cause gastroenteritis by mechanisms unrelated to those involved in epidemic cholera, some of these are shown to harbor gene clusters for cholera toxin (CTX) and toxin coregulated pilus (TCP) that are linked to the virulence potential of V. cholerae O1 or O139 strains. Data available so far suggest that the evolution of pathogenic strains (CTX+ TCP+) of non-O1, non-O139 V. cholerae may follow different mechanisms involving horizontal transfer of Vibrio pathogenicity island (VPI) and CTX gene clusters, exchange of “O” antigen biosynthesis genes, etc.However,mere acquisition of these gene clusters does not necessarily endow a non-O1, non-O139 strain with the ability to cause epidemic form of the diseasewhich probably requires additional genetic traits that are unique to V. cholerae O1 or O139 strains.