Detection of Virulent Vibrio parahaemolyticus Strains from Commercial Shellfish in Shanghai by Loop-mediated Isothermal Amplification

Loop-mediated isothermal amplification(LAMP) was used to detect and analyze virulence-associated genes, thermostable direct hemolysin(tdh) and thermostable-related hemolysin(trh), in Vibrio parahaemolyticus strains isolated from commercial shellfish in Shanghai from August to October, 2014. A total of 180 samples of six common species of shellfish were studied and results were compared between LAMP and polymerase chain reaction(PCR) assays. The detection rates of tdh and trh genes in Vibrio parahaemolyticus strains from commercial shellfish were 12.77% and 11.66% using LAMP as compared to 10.55% and 7.77% by PCR, respectively. Serotyping the isolated virulent strains revealed two O3: K6 serotype Vibrio parahaemolyticus strains, including one carrying double-positive virulence genes(tdh+/trh+). Additionally, high similarity was observed between pulsed-field gel electrophoresis(PFGE) bands of two O3: K6 serotype Vibrio parahaemolyticus strains(similarity 90%). The results indicate contamination of commercial shellfish in Shanghai by virulent strains of Vibrio parahaemolyticus, where the emergence of tdh+/trh+ O3:K6 serotype Vibrio parahaemolyticus is a cause for concern. Surveillance needs to be strengthened, for Vibrio parahaemolyticus strains of different serotypes, especially the O3: K6 serotype. Results from the comparison with PCR assay indicated that LAMP method was suitable for the detection of virulent strains of Vibrio parahaemolyticus in shellfish.