The South Atlantic accounted for 3.4% of Eastern oyster production with the majority of that coming from wild harvest leaving the oysters aquaculture almost unexploited. The occurrence of Vibrio vulnificus and Vibrio parahaemolyticus in South Atlantic aquaculture has not been addressed. In this study, the presence, distribution and dynamics of these pathogens were evaluated at two sites cultivating triploid Grassostrea virginica in floating gear. V. vulnificus and V. parahaemolyticus were detected using primers with TaqMan probes for vvhA gene, and tlh, trh, and tdh genes, respectively. 16S rRNA gene was used for calculating their abundance.
The highest concentration of tlh gene was observed in sediments with three seasonal peaks in May, July, and September at 1.5-5.0×105 copies/g. Much lower concentrations of tlh were detected in water column with peaks at 1.0-1.5×103copies /mL in June and September. Concentration of tlh in oysters was higher than in water, lower than in sediment, and peaked in September at ~1×105 copies /g. These concentrations positively correlated both temporally and spatially; and the temperature and dissolved solids were the environmental drivers. No trh or tdh were detected evidencing the absence of pathogenic V. parahaemolyticus strains.
VvhA highest concentration (~1.8×104 copies/g) was observed in oysters at both sites in July (Fig. 1). Lower concentrations (0.5-1.5×104 copies/g) were observed in sediments with main peak occurred in June (Fig. 2). The lowest vvhA concentrations were detected in water column, which peaked at 15-30 copies/mL in June-July at both sites (Fig. 3). This dynamic and corresponding increase in vvhA abundancy in oysters’ microbiota suggested repositioning of V. vulnificus from sediments to water column, and its bioaccumulation from there by oysters in subsequent months. Temperature, dissolved solids, and turbidity were environmental drivers for vvhA. Since all V. vulnificus are considered pathogenic, its presence in, and possible bioaccumulation by oysters need to be addressed in aquaculture.