In this study, 77 clinical and 67 oyster Vibrio parahaemolyticus isolates from North America were examined for biochemical profiles, serotype, and the presence of potential virulence factors ( tdh , trh , and type III secretion system [T3SS] genes). All isolates were positive for oxidase, indole, and glucose fermentation, consistent with previous reports. The isolates represented 35 different serotypes, 9 of which were shared by clinical and oyster isolates. Serotypes associated with pandemic strains (O1:KUT, O1:K25, O3:K6, and O4:K68) were observed for clinical isolates, and 7 (9%) oyster isolates belonged to serotype O1:KUT. Of the clinical isolates, 27% were negative for tdh and trh , while 45% contained both genes. Oyster isolates were preferentially selected for the presence of tdh and/or trh ; 34% contained both genes, 42% had trh but not tdh , and 3% had tdh but not trh . All but 1 isolate (143/144) had at least three of the four T3SS1 genes examined. The isolates lacking both tdh and trh contained no T3SS2α or T3SS2β genes. All clinical isolates positive for tdh and negative for trh possessed all T3SS2α genes, and all isolates negative for tdh and positive for trh possessed all T3SS2β genes. The two oyster isolates containing tdh but not trh possessed all but the vopB2 gene of T3SS2α, as reported previously. In contrast to the findings of previous studies, all strains examined that were positive for both tdh and trh also carried T3SS2β genes. This report identifies the serotype as the most distinguishing feature between clinical and oyster isolates. Our findings raise concerns about the reliability of the tdh , trh , and T3SS genes as virulence markers and highlight the need for more-detailed pathogenicity investigations of V. parahaemolyticus .

Vibriosis is a leading cause of seafood-associated morbidity and mortality in the United States. Typically associated with consumption of raw or undercooked oysters, vibriosis associated with clam consumption is increasingly being reported. However, little is known about the prevalence of Vibrio spp. in clams. The objective of this study was to compare the levels of Vibrio cholerae , Vibrio vulnificus , and Vibrio parahaemolyticus in oysters and clams harvested concurrently from Long Island Sound (LIS). Most probable number (MPN)–real-time PCR methods were used for enumeration of total V. cholerae , V. vulnificus , V. parahaemolyticus , and pathogenic ( tdh ⁺ and/or trh ⁺ ) V. parahaemolyticus . V. cholerae was detected in 8.8% and 3.3% of oyster ( n = 68) and clam ( n = 30) samples, with levels up to 1.48 and 0.48 log MPN/g in oysters and clams, respectively. V. vulnificus was detected in 97% and 90% of oyster and clam samples, with median levels of 0.97 and −0.08 log MPN/g, respectively. V. parahaemolyticus was detected in all samples, with median levels of 1.88 and 1.07 log MPN/g for oysters and clams, respectively. The differences between V. vulnificus and total and pathogenic V. parahaemolyticus levels in the two shellfish species were statistically significant ( P < 0.001). These data indicate that V. vulnificus and total and pathogenic V. parahaemolyticus are more prevalent and are present at higher levels in oysters than in hard clams. Additionally, the data suggest differences in vibrio populations between shellfish harvested from different growing area waters within LIS. These results can be used to evaluate and refine illness mitigation strategies employed by risk managers and shellfish control authorities.

Vibrio parahaemolyticus is the leading cause of seafood-borne infections in the United States. We report complete genome sequences for two V. parahaemolyticus strains isolated in 2007, CDC_K4557 and FDA_R31 of clinical and oyster origin, respectively. These two sequences might assist in the investigation of differential virulence of this organism.

Vibrio parahaemolyticus is the most common cause of seafood-borne illness reported in the United States. Draft genomes of 132 North American clinical and oyster V. parahaemolyticus isolates were sequenced to investigate their phylogenetic and biogeographic relationships. The majority of oyster isolate sequence types (STs) were from a single harvest location; however, four were identified from multiple locations. There was population structure along the Gulf and Atlantic Coasts of North America, with what seemed to be a hub of genetic variability along the Gulf Coast with some of the same STs occurring along the Atlantic Coast and one shared between the coastal waters of the Gulf and those of Washington state. Phylogenetic analyses found nine well-supported clades. Two clades were composed of isolates from both clinical and oyster sources. Four were composed entirely from clinical sources and three entirely from oyster sources. Each single source clade consisted of one ST. Some human isolates lack tdh and trh and some T3SS genes, which are established virulence genes of V. parahaemolyticus. Thus, these genes are not essential for pathogenicity. However, isolates in the monophyletic groups from clinical sources were enriched in several categories of genes when compared to those from monophyletic groups of oyster isolates. These functional categories include: cell signaling, transport, and metabolism. Identification of genes in these functional categories provides a basis for future in-depth pathogenicity investigations of V. parahaemolyticus. IMPORTANCEVibrio parahaemolyticus is the most common cause of seafood-borne illness reported in the United States and is frequently associated with shellfish consumption. This study contributes to our knowledge of the biogeography and functional genomics of this species around North America. STs shared between the Gulf Coast and the Atlantic seaboard as well as Pacific waters suggests possible transport via oceanic currents or large shipping vessels. STs frequently isolated from humans, but rarely if ever from the environment, are likely more competitive in the human gut compared to other STs. This could be due to additional functional capabilities in areas like cell signaling, transport, and metabolism which may give these isolates an advantage in novel nutrient replete environments like the human gut.