Persistence of Vibrio vulnificus in tissues of Gulf Coast oysters, Crassostrea virginica, exposed to seawater disinfected with UV light

Abstract

Vibrio vulnificus is an estuarine bacterium which can cause opportunistic infections in humans consuming raw Gulf Coast oysters, Crassostrea virginica. Although V. vulnificus is known as a ubiquitous organism in the Gulf of Mexico, its ecological relationship with C. virginica has not been adequately defined. The objective of the present study was to test the hypothesis that V. vulnificus is a persistent microbial flora of oysters and unamenable to traditional methods of controlled purification, such as UV light depuration. Experimental depuration systems consisted of aquaria containing temperature- controlled seawater treated with UV light and 0.2-μm-pore-size filtration. V. vulnificus was enumerated in seawater, oyster shell biofilms, homogenates of whole oyster meats, and tissues including the hemolymph, digestive region, gills, mantle, and adductor muscle. Results showed that depuration systems conducted at temperatures greater than 23°C caused V. vulnificus counts to increase in oysters, especially in the hemolymph, adductor muscle, and mantle. Throughout the process, depuration water contained high concentrations of V. vulnificus, indicating that the disinfection properties of UV radiation and 0.2-μm-pore-size filtration were less than the rate at which V. vulnificus was released into seawater. Approximately 105 to 106 V. vulnificus organisms were released from each oyster per hour, with 0.05 to 35% originating from shell surfaces. These surfaces contained greater than 103 V. vulnificus organisms per cm2. In contrast, when depuration seawater was maintained at 15°C, V. vulnificus was not detected in seawater and multiplication in oyster tissues was inhibited.