Vibrio parahaemolyticus (Vp) is a marine bacterium capable of causing severe gastroenteritis in humans, usually through the consumption of raw shellfish. Before 1995, Vp-vibriosis was sporadic world-wide and caused by a relatively heterogeneous population of the bacterium. Since then, outbreaks have become more epidemic, with foci of infections traced to seafood harvested from single or geographically-linked sites. While initial outbreaks in Asia (and later in South America and the U.S. Gulf Coast region) have been attributed to a single serotypically-related pandemic clonal complex, other serotypes have been implicated in distinct geographical areas, including the Pacific Northwest and Alaska in the U.S.

Current risk assessment models are based on the presence of the virulence-associated genes tdh and trh, yet illnesses have been attributed to tdh- and/or trh- isolates. Previous phylogenetic studies have shown that Vp, like most Vibrio spp., is a genetically diverse species, and as yet there has been no definitive conclusion as to what genes are essential for virulence. Using phenotypic, genetic, and genomic comparison methods such as Multi-Locus Sequence Typing (MLST), we are examining the hypothesis that a set of highly-virulent clones of Vp with increased pathogenic potential have recently emerged in the PNW, and determining whether the emergence can be correlated with specific environmental parameters. MLST and other genotyping analyses of clinical and environmental Vp isolates from PNW sources demonstrate the extensive patterns of diversity as seen elsewhere. However, the majority of PNW strains obtained from human infections form a distinct clonal complex separate from most environmental isolates. Interestingly, many environmental isolates obtained from PNW sources are phylogenetically related to the pandemic clonal complex, but this group has not been associated with clinical infections in the region. Genome sequences.