ECOLOGICAL AND EXPOSURE ASSESSMENT OF VIBRIO VULNIFICUS AND VIBRIO PARAHAEMOLYTICUS IN AREAS OF IMPORTANCE FOR HUMAN USE IN CHESAPEAKE BAY

Abstract

Current microbial surveillance of water quality in marine and estuarine environments focuses on fecal indicator concentrations to determine suitable conditions for swimming or fishing, including commercial harvest of seafood. However, there are many pathogens in our waters, such as Vibrio vulnificus and V. parahaemolyticus, and it remains unclear how well fecal indicator surveillance protects the public from infection. This dissertation studied V. vulnificus and V. parahaemolyticus at locations in Chesapeake Bay where human contact is likely, in order to quantify dermal transmission to humans, describe the impact of storms on pathogen concentrations in oysters, and quantify antimicrobial resistance. Swim studies at four public beaches in Chesapeake Bay in 2009 and 2011 were the first of their kind to quantify Vibrio exposure by recreating swimmers and to qualify exposure in terms of dermal dose. Estimated exposures correlated with surface water Vibrio concentrations and suggested that the public could be exposed to V. vulnificus and V. parahaemolyticus at rates that may cause illness. To better protect human health, estimates of non-consumption dose-response would be helpful in completing a quantitative microbial risk assessment to calculate relative risk of swimming in waters known to harbor Vibrio bacteria.

Oysters, water, and sediment were sampled at an aquaculture facility before and after Hurricane Irene impacted the Chesapeake Bay in 2011. Results indicated no difference in Vibrio uptake between oysters positioned on floats and on bottom sediments, but showed a difference in Vibrio species uptake, with V. parahaemolyticus increasing 1 day post-Irene, unlike V. vulnificus. This study suggests that storm events may increase V. parahaemolyticus in oyster tissue, and that virulent sub-types of both Vibrio species may increase in percent abundance within oysters following a storm event.

Antimicrobial susceptibility testing showed that a large percentage of isolates from surface waters in the Chesapeake Bay displayed intermediate resistance to chloramphenicol. Most antimicrobial agents recommended for treatment of Vibrio illness by CDC were effective at controlling growth of V. vulnificus and V. parahaemolyticus. Results suggest treatment of pediatric illness with trimethoprim-sulfamethoxazole and the aminoglycoside, gentamicin, which was the only aminoglycoside 100% effective in controlling Vibrio growth in this study.