Genomic Features of Environmental and Clinical Vibrio parahaemolyticus Isolates Lacking Recognized Virulence Factors Are Dissimilar

Abstract

ABSTRACT Vibrio parahaemolyticus is a bacterial pathogen that can cause illness after the consumption or handling of contaminated seafood. The primary virulence factors associated with V. parahaemolyticus illness are thermostable direct hemolysin (TDH) and Tdh-related hemolysin (TRH). However, clinical strains lacking tdh and trh have recently been isolated, and these clinical isolates are poorly understood. To help understand the emergence of clinical tdh - and trh -negative isolates, a genomic approach was used to comprehensively compare 4 clinical tdh - and trh -negative isolates with 16 environmental tdh - and trh -negative isolates and 34 clinical isolates positive for tdh or trh , or both, with the objective of identifying genomic features that are unique to clinical tdh - and trh -negative isolates. The prevalence of pathogenicity islands (PAIs) common to clinical isolates was thoroughly examined in each of the clinical tdh - and trh -negative isolates. The tdh PAI was not present in any clinical or environmental tdh - and trh -negative isolates. The trh PAI was not present in any environmental isolates; however, in clinical tdh - and trh -negative isolate 10-4238, the majority of the trh PAI including a partial trh1 gene was present, which resulted in reclassification of this isolate as a tdh -negative and trh -positive isolate. In the other clinical tdh - and trh -negative isolates, neither the trh gene nor the trh PAI was present. We identified 862 genes in clinical tdh - and trh -negative isolates but not in environmental tdh - and trh -negative isolates. Many of these genes are highly homologous to genes found in common enteric bacteria and included genes encoding a number of chemotaxis proteins and a novel putative type VI secretion system (T6SS) effector and immunity protein (T6SS1). The availability of genome sequences from clinical V. parahaemolyticus tdh - and trh -negative isolates and the comparative analysis may help provide an understanding of how this pathotype is able to survive in vivo during clinical illness.