Molecular characterization and genetic diversity study of Vibrio parahaemolyticus isolated from aquaculture farms in India

Vibrio parahaemolyticus is known to cause disease and infection in humans. This study was conducted to understand the prevalence of V. parahaemolyticus and the presence of virulence factors in environmental isolates of V. parahaemolyticus, collected from three major shrimp producing states viz, West Bengal, Andhra Pradesh and Gujarat of India during February 2014 to June 2017. Total 183 V. parahaemolyticus were isolated from moribund shrimp and identified using toxR and 16S rRNA gene. Polymerase Chain Reaction (PCR) was performed to detect virulence genes under T3SS1 and T3SS2 along with AHPND. All the isolates showed presence of vcrD1, vp1680 and vopD1 gene under T3SS1 but negative for AHPND. Only 3% of isolates showed presence of all the virulence genes (vcrD2, vopD2, vopB2 and vopC) used in the present study under T3SS2. The isolates were also tested for the presence of tdh, trh or both the genes; 8% of the isolates had trh gene and 3% of the isolates had tdh gene. The genetic diversity within and between V. parahaemolyticus isolated from three different geographical locations, was analyzed by using 16S rRNA gene. Though the biotype diversity (h) was high for all three populations, phylogenetic study of V. phaemolyticus revealed an admixture of biotypes. Tajima's D (-2.59470; p < .001) test of selective neutrality and Fu's Fs (- 32.422; p < .001) test were negative and significant, suggesting a sudden population expansion with limited time for population differentiation.