Clonal dissemination of Vibrio parahaemolyticus displaying similar DNA fingerprint but belonging to two different serovars (O3 : K6 and O4 : K68) in Thailand and India

Active surveillance of Vibrio parahaemolyticus infection among hospitalized patients in Calcutta, India, showed the appearance of the O4:K68 serovar f or the: first time in March 1998 alongside the continued predominant incide nce of the O3:K6 serovar. Strains belonging to both these serovars have bee n reported to possess pandemic potential. The genomes of O3:K6 and O4:K68 s trains and for comparison, non-O3:K6 and non-O4:K68 strains isolated from t wo different countries, India and Thailand, were examined by different mole cular techniques to determine their relatedness. The O3:K6 and O4:K68 strai ns from Calcutta and Bangkok carried the tdh gene but not the trh gene. Cha racterization of representative strains of these two serovars by ribotyping and by arbitrarily primed-polymerase chain reaction (AP-PCR) showed that t he isolates had identical ribotype and DNA fingerprint. Pulsed-field gel el ectrophoresis (PFGE) performed with the same set of strains yielded nearly similar restriction fragment length polymorphism (RFLP) patterns for the O3 :K6 and O4:K68 isolates from Calcutta and Thailand. Phylogenetic analysis o f the NotI RFLP showed that the O3:K6 and O4:K68 strains formed a cluster w ith 78-91% similarity thus indicating close genetic relationship between th e two different serovars isolated during the same time-frame but from widel y separated geographical regions. The non-O3:K6 and non-O4:K68, in contrast , showed different ribotype, AP-PCR and PFGE patterns.