Trends in the genomic epidemiology of Vibrio cholerae O1 isolated worldwide since 1961

• V. cholerae showed resistance to four drugs (erythromycin, streptomycin, trimethoprim/sulfamethoxazole and ampicillin).
• Multidrug resistance among the strains arose between 1977 and 2010.
• MAMA-PCR showed the dominance of ctxB classical genotype strains in the last two epochs.
• A total of 65.7% strains from different geographical regions were clustered as new phage type 27.
• Cluster B explains most of the hybrid toxigenic (ctxB classical/El Tor) pulsotypes.

Here we describe the international scenario of Vibrio cholerae with a comparative analysis of different aspects of typing. Representative V. cholerae strains (n = 108) associated with endemic cholera regions from 29 states of India and worldwide were subjected to microbiological, molecular and phylogenetic study. All of the strains were V. cholerae serogroup O1 biotype El Tor and were typed according to both the new phage (NP) type and Basu & Mukherjee (BM) typing schemes. The predominant phage type was T-27 (NP)/T-4 (BM) (65.7%; n = 71), followed by phage type T-27 (NP)/T-2 (BM) (14.8%; n = 16), T-26 (NP)/T4 (BM) (12.0%; n = 13), T-13 (NP)/T-4 (BM) (2.8%; n = 3), T-20 (NP)/T-4 (BM) (1.9%; n = 2), T-3 (NP)/T-4 (BM) (0.9%; n = 1), T-23 (NP)/T-4 (BM) (0.9%; n = 1) and T-24 (NP)/T-2 (BM) (0.9%; n = 1). Mismatch amplification mutation assay PCR (MAMA-PCR) findings showed the dominance of ctxB El Tor genotype (77.1%; 54/70) from 1961–1991, whilst the next two epochs showed the supremacy of ctxB classical genotype. Multidrug-resistant strains showed resistance to erythromycin, streptomycin, trimethoprim/sulfamethoxazole, norfloxacin and ampicillin. The regional resistance of epidemic clones in India draws a layout of the rapid dissemination of resistance in the past 30 years and the necessity of proper treatment to protect populations at risk.