Presence of CTX gene cluster in environmental non-O1/O139 Vibrio cholerae and its potential clinical significance

Purpose: The aim of this study was to understand the epidemiological linkage of clinical and environmental isolates of Vibrio cholerae and to determine their genotypes and virulence genes content. Materials and Methods: A total of 60 V. cholerae strains obtained from clinical specimens (n = 40) and surface waters (n = 20) were subjected to genotyping using PFGE and determination of their virulence-associated gene clusters. Result: PCR analysis showed the presence of chromosomally located hly and RTX genetic elements in 100% and 90% of the environmental isolates, respectively. The phage-mediated genetic elements such as CTX, TLC and VPI were detected in 5% of the environmental isolates suggesting that the environmental isolates cannot acquire certain mobile gene clusters. A total of 4 and 18 pulsotypes were obtained among the clinical and environmental V. cholerae isolates, respectively. Non-pathogenic environmentally isolated V. cholerae constituted a distinct cluster with one single non-O1, non-O139 strain (EP6) carrying the virulence genes similar to the epidemic strains. This may suggest the possible potential of conversion of non-pathogenic to a pathogenic environmental strain. Conclusions: The emergence of a single environmental isolate in our study containing the pathogenicity genes amongst the diverse non-pathogenic environmental isolates needs to be further studied in the context of V. cholerae pathogenicity sero-coversion.