Pathogenic potential of non-clinical Vibrio parahaemolyticus strains isolated from the aquatic environments in Southern India

Abstract

Purpose: Vibrio parahaemolyticus is a Gram-negative, halophilic bacterium responsible for diarrheal illness in humans upon consumption of contaminated seafood. Recent studies have shown virulence attributes which are usually associated with clinical strains, may also be present in the V. parahaemolyticus strains recovered from environmental sources. With limited information from India, this study aimed to investigate the distribution of these virulence genes in environmental V. parahaemolyticus isolated from coastal environments and seafood along the southern Indian coast. Methods & Materials: In this study, we screened for 33 different genes encoding hemolysins, secretion systems and pathogenicity islands among V. parahaemolyticus isolates (n=128). Further, for representative isolates, we have explored their pathogenic potential by studying the adherence, cytotoxicity ability and expression of virulence genes during infection of HeLa cells. Results: It was observed that 18.75% isolates tested positive for tdh, 7.03% for trh, and 3.90% were found to harbour both tdh and trh genes. The genes of pathogenicity islands which are specific to pandemic clones were detected partially or completely from more than half of the isolates screened [VPaI-1 (55.46%), VPaI-2 (97.65%), VPaI-3 (92.96%), VPaI-4 (74.21%), VPaI-5 (67.18%), VPaI-6 (96.09%), and VPaI-7 (45.31%) of the isolates]. Among the secretion systems, T3SS1 (97.65%), T6SS2 (98.43%), and T6SS1 (65.62%) were identified. Our results also showed no significant difference in adhesion ability compared to reference clinical strain. The cytotoxicity effect on HeLa cells showed consistent results with previous studies. In the qPCR assay, the trh encoding seafood isolates showed 3-fold increase in the expression level of trh and VopC genes. In all the representative isolates, there was a significant difference (P <0.01) in the expression of trh, VopA and VopC genes considering unadhered and adhered cells determined by Students’ t test. Conclusion: This study characterizes the putative virulence attributes, in-vitro pathogenic potential and relative expression of virulence genes of non-clinical V. parahaemolyticus isolates from coastal environments of Southern India. In conclusion, this study demonstrated the potential of these isolates from coastal environments to cause infection in humans and they may also serve as progenitors for the other disease-causing organisms by lateral transfer of virulence genes.