Biochemical, Serological, and Virulence Characterization of Clinical and Oyster Vibrio parahaemolyticus Isolates

Abstract

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 T3SS2␣ or T3SS2␤ genes. All clinical isolates positive for tdh and negative for trh possessed all T3SS2␣ genes, and all isolates negative for tdh and positive for trh possessed all T3SS2␤ genes. The two oyster isolates containing tdh but not trh possessed all but the vopB2 gene of T3SS2␣, as reported previously. In contrast to the findings of previous studies, all strains examined that were positive for both tdh and trh also carried T3SS2␤ 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. Vibrio parahaemolyticus is the leading cause of seafood-associated illness in the United States and is generally associated with the consumption of raw molluscan shellfish (17). Even so, V. parahaemolyticus illnesses are believed to be highly underdiagnosed (143-fold), possibly due to the relatively low hospitalization (22.5%) and fatality (0.9%) rates (36). Another factor that may influence the underdiagnosis is the fact that traditional biochemical identification of V. parahaemolyticus has proven less reliable than molecular identification for clinical and food isolates (8,21). When an isolate is confirmed as V. parahaemolyticus, virulence characterization is typically performed. The virulence of V. parahaemolyticus was initially attributed to the production of a thermostable direct hemolysin (TDH) (15, 26). The TDH is encoded by the tdh gene, and subsequently a related gene, termed the tdhrelated hemolysin (trh), was identified (26). Together, tdh and trh are widely considered the predominant indicators of strain virulence in V. parahaemolyticus (26,37,38). This is substantiated by the prevalence of tdh and/or trh in clinical V. parahaemolyticus isolates and the infrequent detection of these virulence markers in food and environmental samples (9,27,28,35,40).Investigati...

Phenotypic and Genotypic Characterization of Canadian Clinical Isolates of Vibrio parahaemolyticus Collected from 2000 to 2009

“…Most of the strains belonging to serogroups O1 and O4 also were PCR positive for the hemolysin genes trh or tdh, or both (see Table S1 in the supplemental material). Jones et al (10) examined clinical isolates from across North America (July 2006 to November 2007) and oyster isolates collected across the United States in 2007 and found that the predominant serovars were the pandemic strain O1:KUT, followed by O4:K12, the most common serotype observed in human illnesses from the Pacific Northwest (8,10,11). Among the Canadian clinical isolates of V. parahaemolyticus isolated from 2000 to 2009, serovar O4:KII* (O4:K12 is a serotype of this group) was the most common, followed by the pandemic serovar O1:KUT.…”

“…Herein, we describe the use of pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), ribotyping, serotyping, and virulence gene detection by PCR to study in detail the molecular epidemiology of V. parahaemolyticus strains isolated from Canadian patients (3,(9)(10)(11). A retrospective descriptive laboratory analysis of clinical V. parahaemolyticus isolates from across Canada (primarily British Columbia), which is available from the inventory of the National Microbiology Laboratory, Public Health Agency of Canada, was conducted.…”

The First Report of <i>Vibrio parahaemolyticus</i> Strain O10:K60 in Japan, a New Combination of O and K Serotypes Isolated from a Patient with Gastroenteritis

“…Other studies (19)(20)(21) have reported that the tdh gene is encoded and co-regulated with T3SS2a genes, and that the T3SS2b genes have been detected in trh-positive strains. Moreover, all isolates contain T3SS1 (19,20). Thus, the results of the assays for virulence genes in this study are consistent with those of previous reports.…”

“…In addition, the type III secretion system (T3SS) has been investigated as a potential indicator of virulence (15)(16)(17)(18). Most clinical strains contain two nonredundant T3SSs, T3SS1, and T3SS2 (19,20). T3SS2 has been further subdivided into T3SS2a and T3SS2b (21).…”

Prevalence and Genomic Characterization of Vibrio parahaemolyticus isolated from Molluscan Shellfish and their Inhabiting Water of Coastal Karnataka, India

“…parahaemolyticus can be considered ubiquitous in the marine environment (Jones et al, 2012). In the present study we isolated a total of 203 isolates of V. parahaemolyticus from both water and molluscan shellfish samples.…”