Clonal dissemination of <e1>Vibrio parahaemolyticus</e1> displaying similar DNA fingerprint but belonging to two different serovars (O3∶K6 and O4∶K68) in Thailand and India

Active surveillance of <e1>Vibrio parahaemolyticus</e1> infection among hospitalized patients in Calcutta, India, showed the appearance of the O4∶K68 serovar for the first time in March 1998 alongside the continued predominant incidence of the O3∶K6 serovar. Strains belonging to both these serovars have been reported to possess pandemic potential. The genomes of O3∶K6 and O4∶K68 strains and for comparison, non-O3∶K6 and non-O4∶K68 strains isolated from two different countries, India and Thailand, were examined by different molecular techniques to determine their relatedness. The O3∶K6 and O4∶K68 strains from Calcutta and Bangkok carried the <e1>tdh</e1> gene but not the <e1>trh</e1> gene. Characterization of representative strains of these two serovars by ribotyping and by arbitrarily primed-polymerase chain reaction (AP-PCR) showed that the isolates had identical ribotype and DNA fingerprint. Pulsed-field gel electrophoresis (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 of the <e1>Not</e1>I RFLP showed that the O3∶K6 and O4∶K68 strains formed a cluster with 78–91% similarity thus indicating close genetic relationship between the two different serovars isolated during the same time-frame but from widely separated geographical regions. The non-O3∶K6 and non-O4∶K68, in contrast, showed different ribotype, AP-PCR and PFGE patterns.