Population structural analysis of O1 El Tor Vibrio cholerae isolated in China among the seventh cholera pandemic on the basis of multilocus sequence typing and virulence gene profiles

Serogroup O1 Vibrio cholerae is the most common agents to cause epidemic and pandemic cholera disease. In this study, multilocus sequence typing (MLST) was performed on 160 serogroup O1 strains (including 42 toxigenic and 118 non-toxigenic), and the virulence/fitness gene profiles of 16 loci were further analysed for 60 strains of these. Eighty-four sequence types (STs) with 14 clonal complexes were distinguished, and 29 STs were unique. Except SD19771005, all toxigenic strains were well-separated from the non-toxigenic strains. While a group of non-toxigenic strains clustered closer to the toxigenic strains compared to the other strains. Overall the examined gene loci showed higher presence rates in the toxigenic strains compared to the non-toxigenic strains. It is worth noting that the presence rates of VPI, TLC, VSP-I and VSP-II in the non-toxigenic strains that were clustered closer to the toxigenic strains were much higher compared to the other non-toxigenic strains. Our study indicated the complex population structure of O1 strains, and parts of non-toxigenic strains are genetically more closely related to toxigenic strains than other non-toxigenic strains, suggesting that these strains may have a higher potential for infection with CTXФ in the environment or host intestine and is more efficient to become new pathogenic or epidemic clones.