Clonal diversity among recently emerged strains of Vibrio parahaemolyticusO3 : K6 associated with pandemic spread

The genomes of the O3:K6 strains of Vibrio parahaemolyticus which abruptly emerged in Calcutta, India, in February 1996 and which demonstrated an unus ual potential to spread and an enhanced propensity to cause infections were examined by different molecular techniques to determine clonality. No rest riction fragment length polymorphism (RFLP) in the gene encoding the thermo stable direct hemolysin tvas observed among the O3:K6 isolates of V. paraha emolyticus. Clonal diversity among the O3:K6 strains became evident by exam ining the RFLPs of the rrn operons and by the use of pulsed-field gel elect rophoresis. Five ribotypes were distinguished among the O3:K6 strains exami ned, with ribotype R4 constituting the major type. Strains of O3:K6 isolate d between June and August 1996 showed different pulsotypes compared to the pulsotypes of strains isolated before and after this period, indicating gen etic reassortment among these strains, but those isolated be tween August 1 996 and March 1998 showed identical or nearly similar pulsotypes. It is cle ar that there is a certain degree of genomic reassortment among the O3:K6 c lones but that these strains are predominantly one clone.