In situ dynamics of Vibrio parahaemolyticus and Vibrio vulnificus in water, sediment and triploid Crassostrea virginica oysters cultivated in floating gear.

Aims: To understand spatial-temporal distribution of Vibrio parahaemolyticus and Vibrio vulnificus in triploid Crassostrea virginica in off-bottom aquaculture.

Methods And Results: Oysters, sediments and water were seasonally collected in Georgia, USA. V. parahaemolyticus and V. vulnificus were quantified with tlh/tdh/trh and vvhA genes, respectively. No tdh/trh genes were detected. Highest concentrations of tlh gene were observed in summer sediments > oysters > water (10 /g, 10 /g, 10 /ml). VvhA concentrations were similar in sediments and oysters but never exceeded ≥3 × 10 /ml in water. Concentrations of tlh and vvhA genes correlated to temperature and turbidity, respectively, which along with their different spatial distribution indicated different environmental drivers. In oysters, ratios of the tlh and vvhA to 16S rRNA gene have increased from 0 to 10 and 10 in summer, while these ratios in water and sediments were lower by 2-3 orders of magnitude.

Conclusions: Dynamics of tlh and vvhA concentrations and abundances suggested enrichment of V. parahaemolyticus and V. vulnificus by off-bottom triploid oysters in summer resulting in their abundance by far exceeding that in water.

Significance And Impact Of The Study: This first report on enrichment of Vibrio pathogens in triploid oysters with no direct contact to sediments reveals a threat to human health suggesting their monitoring in triploid off-bottom C. virginica aquaculture.