Application of whole genome sequencing in etiology investigation of an outbreak of polyclonal Vibrio parahaemolyticus infection

ObjectiveApplying real-time PCR and whole genome sequencing in the etiology investigation of an outbreak caused by Vibrio parahaemolyticus.

MethodsDiarrhea patient stool samples and epidemiological data were collected. Suspected pathogens were screened with real-time PCR. V. parahaemolyticus strains were isolated, identified and their serotypes were confirmed by agglutination with commercial diagnostic serum. The existences of tdh and trh genes were identified with real-time PCR. The drug resistance of the strains was determined by broth micro-dilution method, and whole genome sequencing data was used for genetic analysis.

ResultsA total of 13 V. parahaemolyticus strains were isolated from 9 anal swabs of patients, including 7 strains of O4∶KUT (trh–/tdh+) and 6 trains of O1∶KUT (5 trh+/tdh+ strains, 1 trh–/tdh–strain). All the V. parahaemolyticus strains were only resistant to ampicillin and sensitive to other 29 kinds of antibiotics. The 13 V. parahaemolyticus strains formed four independent and distant related lineages, Lineage 1 (O4∶KUT, trh–/tdh+, 2 strains), Lineage 2 (trh–/tdh–, 1 strain), Lineage 3 (O1∶KUT trh+/tdh+, 5 strains) and Lineage 4 (O4∶KUT, trh–/tdh+, 5 strains). Three patients had mixed infections of V. parahaemolyticus from three different genetic branches.

ConclusionThis outbreak was caused by polyclonal V. parahaemolyticus. Whole genome sequencing has a good application prospect in pathogen analysis of diarrhea outbreak.