A variety of serovars of the food-borne pathogen Vibrio parahaemolyticus normally cause infection. Since1996, 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 otherbiological 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 relatedpatterns, with I1(81%) and I5(13%) being the most frequent patterns. Pattern I1 was the major one for strainsfrom 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 nonO3: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 therecently isolated O3:K6 strains.