Purpose: The goal of this project was to identify T3SS-2 EPs involved in the enterotoxigenicity of Vp and to determine their distribution and relationship to other virulence markers.
Methods: In silico analysis was performed on sequenced T3SS-2 PI regions, for which two variants have been reported, α and β. Fourteen putative EP encoding genes were identified, many with an α and β allele. PCR primers were designed to identify alleles, if present. Serotyping of the O and K antigens was performed using commercial antisera. A total of 186 Vp strains, which included clinical and environmental isolates, were analyzed for all targets, and for urease activity (UA).
Results: Among O3:K6 or UT:K6 clinical strains that only possessed tdhA, only α-EP gene targets were present. An environmental variant of this PI type was observed in O5 strains. Additionally, some strains possessed UA in the absence of trh. For strains which possessed trh, with or without tdhA, only the β alleles of EP genes were present (T3SS-2β PI), except for two adjacent α-allele EP genes, which was observed in some strains. A variant of T3SS-2β PI which had EP gene β-alleles and UA in the absence of tdhA and trh was observed in some O1, O3, O5, and O8 strains.
Significance: These results suggest that T3SS-2 PI variants exist. Further, the synergistic contributions of T3SS-2 EPs with other virulence markers needs to be investigated, in vivo, to understand the enterotoxigenicity of V. parahaemolyticus.