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

Vibrio parahaemolyticus is a bacterial pathogen that can cause illness after the consumption or handling of contaminated seafood. The primary virulence factors associated withV. parahaemolyticus illness are thermostable direct hemolysin (TDH) and Tdh-related hemolysin (TRH). However, clinical strains lackingtdh andtrh have recently been isolated, and these clinical isolates are poorly understood. To help understand the emergence of clinicaltdh - andtrh -negative isolates, a genomic approach was used to comprehensively compare 4 clinicaltdh - andtrh -negative isolates with 16 environmentaltdh - andtrh -negative isolates and 34 clinical isolates positive fortdh ortrh , or both, with the objective of identifying genomic features that are unique to clinicaltdh - andtrh -negative isolates. The prevalence of pathogenicity islands (PAIs) common to clinical isolates was thoroughly examined in each of the clinicaltdh - andtrh -negative isolates. Thetdh PAI was not present in any clinical or environmentaltdh - andtrh -negative isolates. Thetrh PAI was not present in any environmental isolates; however, in clinicaltdh - andtrh -negative isolate 10-4238, the majority of thetrh PAI including a partialtrh1 gene was present, which resulted in reclassification of this isolate as atdh -negative andtrh -positive isolate. In the other clinicaltdh - andtrh -negative isolates, neither thetrh gene nor thetrh PAI was present. We identified 862 genes in clinicaltdh - andtrh -negative isolates but not in environmentaltdh - andtrh -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 clinicalV. parahaemolyticus tdh - andtrh -negative isolates and the comparative analysis may help provide an understanding of how this pathotype is able to survivein vivo during clinical illness.