Epidemiol. Infect. zyxwvutsrqponmlkji (1998), zyxwvutsrq 121, 259-268. Printed in the United Kingdom zyxwvu 0 1998 Cambridge University Press zyxw Phenotypic and molecular characterization of Vibrio zyx cholerae 01 isolated in Samutsakorn, Thailand before, during and after the emergence of V. cholerae 0139 A. DALSGAARD1*, 0. SERICHANTALERGS', A. FORSLUNDl, C. PITARANGSI' AND P. ECHEVERRIA' zyxwvutsr Department zyxwvutsrqp of Veterinary Microbiology, The Royal Veterinary and Agricultural University, DK-I870 Frederiksberg C, Denmark 'Armed Forces Research Institute of Medical Sciences, 31.516 Ratcha Withi Rd, 10400 Bangkok, Thailand (Accepted 20 May 2998) SUMMARY Seventy clinical strains of Vibrio cholerae 01 isolated from 1982-96 in Samutsakorn, a port city 30 km southwest of Bangkok where cholera occurs at low levels with regular seasonality, were characterized to investigate if there were any differences among the 0 1 strains isolated before, during and after the 0 139 epidemic. Pulsed-field gel electrophoresis (PFGE) typing, ribotyping and southern blot hybridization with a cholera toxin probe (CT genotyping) demonstrated several genotypes among 0 1 strains isolated before the emergence of V. cholerae 0139. However, 01 strains isolated during and after the advent of 0139 showed identical ribotypes which were distinctly different from the types identified in strains isolated before the emergence of 0139. Ribotypes identified in strains during and after the advent of 0139 were also demonstrated by 01 strains isolated immediately before the emergence of 0139. Considering the seasonality of cholera in Samutsakorn, the identical ribotype and CT genotype and the closely related PFGE types shown by all 0 1 strains isolated during and after the appearance of 0139 is remarkable and suggest that the V. cholerae 0 1 strain may reemerge from an environmental source. A subgroup of V. cholerae 01 strains isolated before the emergence of the 0139 epidemic had a ribotype identical to a type demonstrated by 0139 strains isolated in Thailand. Our results support similar findings in Bangladesh and India that a distinct 01 strain appeared during the 0139 epidemic. However, compared with the apparent identical strain which replaced 0139 in Bangladesh and India, the emerged 0 1 strain in Samutsakorn showed a different ribotype and CT genotype. [3]. However, compared to India and Bangladesh were the 0139 serotype displaced V. cholerae 01 causing an INTRODUCTION In early 1993, Vibrio cholerae 0139 Bengal was increase in the total number of cholera cases, the 0139 identified for the first time in Thailand and rapidly serotype established itself in Samutsakorn together spread within the country [l, 21. Samutsakorn, a with V. cholerae 01 with no increase in the total major port city located near Bangkok, is one of the number of cholera cases reported [3-51. Most sur- few locations in Thailand where cholera occurs with prisingly, just after 10 months of its appearance in regular seasonality, although at relatively low levels Samutsakorn in August 1993 the prevalence of V. cholerae 0139 decreased dramatically [3, 61. A similar z * Author for correspondence: Department of Veterinary Micro- decrease in the prevalence of V. cholerae 0139 was biology, Biilowsvej 13, DK-1870 Frederiksberg C, The Royal Veterinary and Agricultural University, Denmark. reported in Bangladesh where the 01 serotype