Uptake and depuration of the C- and E-genotypes of Vibrio vulnificus by the Eastern Oyster (Crassostrea virginica)

Abstract

The human pathogen Vibrio vulnificus is a Gram-negative estuarine bacterium that infect via wounds and ingestion, and is the leading cause of seafood-borne death in the United States. Vibrio vulnificus is part of the naturally occurring flora of both estuaries and estuarine mollusks (especially oysters). Vibrio vulnificus is divided into two genotypes, including a clinically associated C-type, and an environmentally associated E-type that is more rarely involved in septicemia. These two genotypes are found in a nearly even ratio in the aquatic environment, but oysters harvested from those very environments show a V. vulnificus genotype ratio disparity, with 87% of the species being that of the E-genotype. To determine if oysters selectively incorporate E-types over C-types, we placed oysters in water inoculated with either C- or E-type V. vulnificus strains that were phenotypically different from the normal flora and measured the uptake and depuration over a course of 6 days. We found significantly greater uptake, but equally effective depuration, of C-type V. vulnificus in oyster gill tissue, mantle tissue and whole oyster homogenates. Because uptake of the C-genotype was generally greater than the E-genotype, it appears unlikely that simple selective uptake is the cause of E-type V. vulnificus predominating in oysters.