Population Structure of Clinical and Environmental <em>Vibrio parahaemolyticus</em> from the Pacific Northwest Coast of the United States

<div><p><em>Vibrio parahaemolyticus</em> is a common marine bacterium and a leading cause of seafood-borne bacterial gastroenteritis worldwide. Although this bacterium has been the subject of much research, the population structure of cold-water populations remains largely undescribed. We present a broad phylogenetic analysis of clinical and environmental <em>V. parahaemolyticus</em> originating largely from the Pacific Northwest coast of the United States. Repetitive extragenic palindromic PCR (REP-PCR) separated 167 isolates into 39 groups and subsequent multilocus sequence typing (MLST) separated a subset of 77 isolates into 24 sequence types. The Pacific Northwest population exhibited a semi-clonal structure attributed to an environmental clade (ST3, N = 17 isolates) clonally related to the pandemic O3:K6 complex and a clinical clade (ST36, N = 20 isolates) genetically related to a regionally endemic O4:K12 complex. Further, the identification of at least five additional clinical sequence types (i.e., ST43, 50, 65, 135 and 417) demonstrates that <em>V. parahaemolyticus</em> gastroenteritis in the Pacific Northwest is polyphyletic in nature. Recombination was evident as a significant source of genetic diversity and in particular, the <em>rec</em>A and <em>dtd</em>S alleles showed strong support for frequent recombination. Although pandemic-related illnesses were not documented during the study, the environmental occurrence of the pandemic clone may present a significant threat to human health and warrants continued monitoring. It is evident that <em>V. parahaemolyticus</em> population structure in the Pacific Northwest is semi-clonal and it would appear that multiple sequence types are contributing to the burden of disease in this region.</p>