Molecular characteristics of clinical isolates of Vibrio parahaemolyticus serogroup O4 in Hangzhou, Zhejiang, 2013−2018

  Objective  To analyze molecular characteristics of Vibrio parahaemolyticus serogroup O4 in diarrhea patients in Hangzhou, Zhejiang province.

  Methods  A total of 1 061 V. parahaemolyticus strains isolated from samples of diarrhea cases in Hangzhou from 2013 to 2018 were serotyped by serum agglutination, and 147 isolates of V. parahaemolyticus serogroup O4 were used to detect the virulence genes of thermostable direct hemolysin (tdh), thermostable hemolysin (trh), thermolabile hemolysin (tlh), toxRS/new genes by qPCR, and pulse-field gel electrophoresis (PFGE) was used.

  Results  The serogroup O4 included O4∶KUT (87.07%, 128/147), O4∶K8 (10.20%, 15/147) and O4∶K9 (2.72%, 4/147). The qPCR results showed that the virulence genes carried by the strains were all tdh⁺trh^-tlh^-toxRS/new^-. The PFGE patterns had two main clusters, PA (mainly isolates after 2016) and PB (isolates from 2013 to 2018), which contained 15 and 16 patterns respectively. All the O4∶K8 strains belonged to PA cluster, and O4∶K9 strains belonged to PB cluster.

  Conclusion  There were two different O4∶ KUT clones in local food-borne isolates in Hangzhou in recent years. The O4∶KUT strains of pattern PB have been detected since 2013. The O4∶KUT strains of pattern PA, which were detected in 2016, have caused food-borne outbreaks since then and have the potential to become a local epidemic clone.