Assessment of Vibrio parahaemolyticus levels in oysters (Crassostrea virginica) and seawater in Delaware Bay in relation to environmental conditions and the prevalence of molecular markers to identify pathogenic Vibrio parahaemolyticus strains

Abstract

This study identified Vibrio parahaemolyticus in oyster and seawater samples collected from Delaware Bay from June through October of 2016. Environmental parameters including water temperature, salinity, dissolved oxygen, pH, and chlorophyll a were measured per sampling event. Oysters homogenate and seawater samples were 10-fold serially diluted and directly plated on CHROMagarᵀᴹ Vibrio medium. Presumptive V. parahaemolyticus colonies were counted and at least 20% of these colonies were selected for molecular chracterization. V. parahaemolyticus isolates (n = 165) were screened for the presence of the species-specific thermolabile hemolysin (tlh) gene, the pathogenic thermostable direct hemolysin (tdh)/ thermostable related hemolysin (trh) genes, the regulatory transmembrane DNA-binding gene (toxR), and V. parahaemolyticus metalloprotease (vpm) gene using a conventional PCR. The highest mean levels of the presumptive V. parahaemolyticus were 9.63×103 CFU/g and 1.85×103 CFU/mL in the oyster and seawater samples, respectively, during the month of July. V. parahaemolyticus levels in oyster and seawater samples were significantly positively correlated with water temperature. Of the 165 isolates, 137 (83%), 110 (66.7%), and 108 (65%) were tlh+, vpm+, and toxR+, respectively. Among the V. parahaemolyticus (tlh+) isolates, 7 (5.1%) and 15 (10.9%) were tdh+ and trh+, respectively, and 24 (17.5%), only oyster isolates, were positive for both genes. Potential pathogenic strains that possessed tdh and/or trh were notably higher in oyster (39%) than seawater (15.6%) isolates. The occurrence of total V. parahaemolyticus (tlh+) was not necessarily proportional to the potential pathogenic V. parahaemolyticus. Co-occurrence of the five genetic markers were observed only among oyster isolates. The co-occurrence of the gene markers showed a relatedness potential of tdh occurrence with vpm. We believe exploring the role of V. parahaemolyticus metalloprotease and whether it is involved in the toxic activity of the thermostable direct hemolysin (TDH) protein can be of significance. The outcomes of this study will provide some foundation for future studies regarding pathogenic Vibrio dynamics in relation to environmental quality.

Genomic and Transcriptomic Analysis Reveal Multiple Strategies for the Cadmium Tolerance in Vibrio parahaemolyticus N10-18 Isolated from Aquatic Animal Ostrea gigas Thunberg

“…V. parahaemolyticus N10-18 isolate was recovered from O. gigas Thunberg [ 23 ]. The bacterium tested negative for the toxic tdh and trh genes but positive for the species-specific gene tlh [ 49 ]. The results also showed that V. parahaemolyticus N10-18 was tolerant to the heavy metals Cd 2+ and Zn 2+ , as well as the antimicrobial agents AMP, KAN, and STR ( Table S1 ).…”

Multilocus Sequence Typing and Virulence Potential of Vibrio parahaemolyticus Strains Isolated from Aquatic Bird Feces

“…This study showed that strains isolated from bird feces possessed tdh ( n = 3), trh ( n = 4), or both tdh and trh ( n = 1). In general, a higher proportion of trh -positive versus tdh -positive V. parahaemolyticus was detected among environmental samples ( 53 – 55 ). In Japan, trh -positive V. parahaemolyticus strains with various serotypes have been isolated from aquatic birds ( 7 ).…”

Incidence, Antibiotic Susceptibility and Characterization of Vibrio parahaemolyticus Isolated from Seafood in Selangor, Malaysia

“…Despite the increased risk of contamination associated with all types of shellfish, the higher density of Vibrio species in short-necked clams can be linked to the filter-feeding habits of these molluscs. Bivalves such as the short-necked clams feed by filtering water through their gills, allowing bacteria and other contaminants to mobilise and concentrate in the digestive tract [13,32,101,102] . However, the findings cannot be extrapolated to all types of bivalve molluscs.…”