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.
Highlights
Vibrio parahaemolyticus is a gram-negative, halophilic, pathogenic bacterium that negatively impact aquatic ecosystems and human health [1,2,3]
Among the physicochemical parameters assessed in this study, water temperature was the only factor that significantly positively correlated with total V. parahaemolyticus level in oyster and seawater samples
The prevalence pattern of the key genes in V. parahaemolyticus isolates from seawater does not reflect the pattern of V. parahaemolyticus isolates from oysters
Summary
Vibrio parahaemolyticus is a gram-negative, halophilic, pathogenic bacterium that negatively impact aquatic ecosystems and human health [1,2,3] They are curved rods, motile with a single polar flagellum and belong to the family Vibrionaceae. V. parahaemolyticus is one of the key causes of gastroenteritis leading to diarrhea, headache, vomiting, and abdominal cramps following the consumption of contaminated food or water. Organisms like oysters which are filter-feeding mollusks, tend to accumulate different microorganisms from seawater during their filtration [7,8,9] They are able to accumulate V. parahaemolyticus 100-fold higher than the surrounding water [8, 9]. V. parahaemolyticus occurrence in oysters can reach 100% [8]
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