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.

Comparative sequence analysis of recA gene among Vibrio cholerae isolates from Iran with globally reported sequences.

AIMS: To study the genetic relatedness between V. cholerae isolates from Iran and other countries based on housekeeping gene recA sequence analysis. METHODS AND RESULTS: A 995-bp region of the recA gene from 24 V. cholerae isolates obtained from human and surface water origins in Iran over a 5-year period was sequenced and compared with the sequence data from the isolates belonging to other places. Cluster analysis of the constructed dendrogram based on recA sequence divergence for our clinical isolates showed one sequence type (ST), whereas environmental isolates revealed eight STs. Interestingly, one of our environmental isolates was intermixed with clinical isolates in the largest cluster containing the epidemic strains. Our 24 isolates plus 198 global isolates available in the GenBank showed 77 sequence types (STs) with at least one nucleotide difference. CONCLUSIONS: Our result suggested that recA sequencing is a reliable analysis method for understanding the relatedness of the local isolates with the isolates obtained elsewhere. SIGNIFICANCE AND IMPACT OF THE STUDY: Understanding the genetic relatedness between V. cholerae isolates could give insights into the health care system for better control and prevention of the cholera.