Genetic variation in potentially virulent Vibrio parahaemolyticus from the northern Gulf of Mexico

Nicholas Felix Noriea III

Abstract

Vibrio parahaemolyticus (Vp ) is a gram-negative bacterium found naturally in marine and estuarine environments. Vp is found in oysters including those which are later consumed by the public. Sub-populations of potentially virulent Vp contain specific virulence factors and are relevant human pathogens capable of causing gastroenteritis, wound infection, and death. The tdh and trh genes, both encoding hemolysins, have been correlated with the majority of clinical Vp isolates but have not been shown to be the definitive virulence factors. A total of 146 Vp isolates from the northern Gulf of Mexico were collected and probed for the presence of specific virulence factors such as tdh, trh , Type III secretion System (T3SS) 1, T3SS2α, T3SS2β, and toxRS . The most representative sub-group of potentially pathogenic Vp were tdh + /trh+ . Isolates containing only tdh were uncommon, and tdh- / trh+ isolates were extremely rare. The distribution of virulence factors in environmental Vp strains was compared with strain fitness through Vp human intestinal epithelial cell cytotoxicity assays and oyster (Crassostrea virginica ) hemocyte bactericidal challenges. The assays were performed to determine significant differences in cytotoxicity or bactericidal survival between pathogen subgroups (tdh+ / trh- , tdh- / trh+ , and tdh- / trh+ ). Significant changes in Vp gene expression were measured for representative clinical strains of the diametric virulence factor sub-groups tdh+ /trh- and tdh- /trh+ . Transcriptomic changes were measured during exposure to human intestinal epithelial cells and oyster hemocyte. Relative changes in the Vp transcriptome were compared both over time and between strain to give significantly regulated genes involved in cytotoxicity and oyster hemocyte bactericidal avoidance.