Molecular characterization of Vibrio parahaemolyticus collected from human infections in Shenzhen, between 2002 and 2008

Abstract

To determine the occurrence and distribution of specific clones of pathogenic Vibrio parahaemolyticus(VP)isolated in Shenzhen and to assess the relationship between serotype O3:K6 and the globally distributed pandemic clone. A total of 1005 VPs isolated from diarrhea patients in 2002-2008 were sero-typed. Real-time PCR was used to detect the virulence genes tlh, toxR, tdh, trh and orf8 in 281 isolates from 68 different serotypes. The main serotypes were typed by pulsed field gel electrophoresis(PFGE). Strains with dominant serotypes and PFGE patterns were assayed by GS-PCR and toxRS sequencing for the identification of pandemic clone. Multilocus sequence typing(MLST)analysis was reserved for exemplary 41 O3 : K6 and O1 : K25 isolates. Seventy-nine serotypes were observed among the 1005 isolates, including O3 : K6(57.9%), O4 : K8(8.16%), O1 : KUT(5.87%), O1 : K25(5.27%), O4 : K68(1.39%), O1 : K56(1.39%) and O9 : K44(0.99%). Most of the strains(99.36%)showed PCR positive to tlh, toxR, and tdh but eleven strains were tdh negative. MLST showed that all the 36 O3 : K6 isolates belonged to ST3 and all the 5 O4 : K8 strains were ST189. These results matched the description of the pandemic VP clone. A recognizable burden of diarrheal illness caused by VP had been seen in Shenzhen. Results from serotyping indicated that although there existing a large variety of diversities, the dominant serotype appeared to be O3 : K6. VP isolates identified in Shenzhen mainly showed as tdh positive but trh negative, in consistent with the current pandemic O3 : K6 clone. The pandemic O3 : K6 clone did appear to co-exist with other clones of O3 : K6, as well as O4 : K8,O1 : K25. Potential outbreak of VP could be monitored through the laboratory-based surveillance programs, suggesting that the strategies related to prevention and control of VP should be prioritized in Shenzhen.