Impact of Hurricane Irene on Vibrio vulnificus and Vibrio parahaemolyticus concentrations in surface water, sediment, and cultured oysters in the Chesapeake Bay, MD, USA

To determine if a storm event (i.e., high winds, large volumes of precipitation) could alter concentrations of Vibrio vulnificus and V parahaemolyticus in aquacultured oysters (Crassostrea virginica) and associated surface water and sediment, this study followed a sampling timeline before and after Hurricane Irene impacted the Chesapeake Bay estuary in late August 2011. Aquacultured oysters were sampled from two levels in the water column: surface (0.3 m) and near-bottom (just above the sediment). Concentrations of each Vibrio spp. and associated virulence genes were measured in oysters with a combination of real-time PCR and most probable number (MPN) enrichment methods, and in sediment and surface water with real-time PCR. While concentration shifts of each Vibrio species were apparent post-storm, statistical tests indicated no significant change in concentration for either Vibrio species by location (surface or near bottom oysters) or date sampled (oyster tissue, surface water, and sediment concentrations). V vulnificus in oyster tissue was correlated with total suspended solids (r = 0.41, P = 0.04), and V vulnificus in sediment was correlated with secchi depth (r = -0.93, P < 0.01), salinity (r = -0.46, P = 0.02), tidal height (r = -0.45, P = 0.03), and surface water V vulnificus (r = 0.98, P < 0.01). V parahaemolyticus in oyster tissue did not correlate with environmental measurements, but V parahaemolyticus in sediment and surface water correlated with several measurements including secchi depth [r = -0.48, P = 0.02 (sediment); r = -0.97, P < 0.01 (surface water)] and tidal height [r = -0.96, P < 0.01 (sediment), r = -0.59, P < 0.01 (surface water)]. The concentrations of Vibrio spp. were higher in oysters relative to other studies (average V vulnificus 4 x 10(5) MPN g(-1), V parahaemolyticus 1 x 10(5) MPN g(-1)), and virulence-associated genes were detected in most oyster samples. This study provides a first estimate of storm-related Vibrio density changes in oyster tissues, sediment, and surface water at an aquaculture facility in the Chesapeake Bay.