Emergence of classical ctxB genotype 1 and tetracycline resistant strains of Vibrio cholerae O1 El Tor in Assam, India.

Cholera epidemics with moderately high case fatality rates in Assam, northeast India were investigated in 2007, 2008 and 2010. Based on mismatch amplification mutation assay PCR for detection of ctxB allele, 40 isolates of Vibrio cholerae O1 El Tor collected from the epidemics were found to harbour the classical ctxB gene allele of cholera toxin (CT). DNA sequencing of ctxB gene confirmed the isolates to be genotype 1 of ctxB. Antimicrobial susceptibility tests reveal that 100% of the isolates were resistant to trimethoprim and 40% were resistant to tetracycline. The recent V. cholerae O1 strains circulating in Assam, India are due to the El Tor variant carrying classical type CT. Emergence of tetracycline and trimethoprim resistant strains necessitates the review of antibiotic use for severe cholera.