Presence of T3SS2β genes in trh⁺ Vibrio parahaemolyticus isolated from seafood harvested along Mangalore coast, India

Abstract

Vibrio parahaemolyticus is a seafood-borne pathogen autochthonous to the marine and estuarine ecosystem, responsible for gastroenteritis when contaminated raw seafood is consumed. The pathogenicity has been associated with thermostable direct haemolysin (TDH) and TDH-related haemolysin (TRH). Of late, the presence of T3SS2α and T3SS2β gene clusters has been well documented in clinical isolates of Vibrio parahaemolyticus and known to play an essential role in pathogenesis. However, reports on the presence of T3SSβ genes in V. parahaemolyticus isolated from the seafood and/or environmental samples are scanty. In this study, we have identified and analysed the distribution of the T3SS2β genes in V. parahaemolyticus isolated from seafood harvested along southwest coast of India. Results showed that T3SS2β genes are solely associated with trh⁺ and tdh⁺ /trh⁺ strains of V. parahaemolyticus. Reverse transcriptase PCR (RT-PCR) showed that the T3SS2β genes identified in trh⁺ V. parahaemolyticus were transcriptionally active. To our knowledge, this study appears to be the first description on the presence of T3SS2β-positive V. parahaemolyticus isolated from seafood in India. The study of T3SS2 along with other virulence factors will help in better understanding of the risk of seafood-borne illness due to V. parahaemolyticus.

Significance and impact of the study: T3SSs (α or β) are the important virulence factors of Vibrio parahaemolyticus that contribute to their pathogenicity in humans. This study demonstrated the presence of T3SS2β genes in V. parahaemolyticus isolated from the seafood harvested along Mangalore coast. RT-PCR showed that the T3SS2β genes identified in seafood isolates of V. parahaemolyticus were found to be functional. To the best of our knowledge, this is the first description of T3SS2β genes in trh⁺ V. parahaemolyticus isolated from seafood in India. The presence of T3SS2 along with other virulence factors such as TDH and/or TRH highlights a potential health risk for seafood consumers.

Keywords: TDH-related haemolysin; V. parahaemolyticus; seafood; thermostable direct haemolysin; type III secretion system.