Characterization of Vibrio cholerae O139 belonging to multiple ribotypes and isolated from diarrhoeal patients in Kerala, southern India

Twenty-four Vibrio cholerae O139 strains isolated from Kerala, southern India were characterized by PCR, CTX typing and ribotyping; all of which, except three strains, carried the core of the CTX genetic element, colonization-toxin co-regulated pilus, the adherence outer membrane protein, haemolysin, central regulatory protein encoded toxR, SXT genetic element, and produced cholera toxin and biofilm. Results of RFLP analysis revealed twenty-one of the O139 strains possess two copies of CTXΦ and pre-CTXФ always preceded by tandemly arranged RS1 element; one had two copies of pre-CTXΦ and two a single copy of pre-CTXΦ. Nucleotide sequencing detected classical ctxB in CTXETΦ and CTXCalcФ with additional change at 28th amino acid position of CTXCalcФ. Ribotype analysis revealed the presence of multiple ribotypes, including B-I and B-II, and new ribotypes designated B-VIIIa, B-VIIIb and B-IX, not reported earlier among V. cholerae O139 strains. These observations thus indicate that genetic recombination or mutations had occurred in conserved rrn operon and variations in CTXΦ may have implications on the evolution of the organism.

Research highlights▶ All of the 24 Vibrio cholerae O139 strains, except three strains, carried the virulence, regulatory and SXT genes. ▶ Twenty-one O139 strains possess two copies of CTXΦ and pre-CTXФ; one had two copies of pre-CTXΦ and two a single copy of pre-CTXΦ. ▶ Classical ctxB was detected in CTXETΦ and CTXCalcФ with additional change at 28th amino acid position in CTXCalcФ. ▶ Multiple ribotypes, included new ribotypes designated B-VIIIa, B-VIIIb and B-IX, was reported among V. cholerae O139 strains.