Characteristics of Vibrio parahaemolyticus O3:K6 from Asia.

A variety of serovars of the food-borne pathogen Vibrio parahaemolyticus normally cause infection. Since 1996, the O3:K6 strains of this pathogen have caused pandemics in many Asian countries, including Taiwan. For a better understanding of these pandemic strains, the recently isolated clinical O3:K6 strains from India, Japan, Korea, and Taiwan were examined in terms of pulsed-field gel electrophoresis (PFGE) typing and other biological characteristics. After PFGE and cluster analysis, all the O3:K6 strains were grouped into two unrelated groups. The recently isolated O3:K6 strains were all in one group, consisting of eight closely related patterns, with I1(81%) and I5(13%) being the most frequent patterns. Pattern I1 was the major one for strains from Japan, Korea, and Taiwan. All recently isolated O3:K6 strains carried the thermostable direct hemolysin (tdh) gene. No significant difference was observed between recently isolated O3:K6 strains and either non-O3:K6 reference strains or old O3:K6 strains isolated before 1996 with respect to antibiotic susceptibility, the level of thermostable direct hemolysin, and the susceptibility to environmental stresses. Results in this study confirmed that the recently isolated O3:K6 strains of V. parahaemolyticus are genetically close to each other, while the other biological traits examined were usually strain dependent, and no unique trait was found in the recently isolated O3:K6 strains.