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DIFFERENTIAL EFFECTS OF OYSTER (CRASSOSTREA VIRGINICA) DEFENSES ON CLINICAL AND ENVIRONMENTAL ISOLATES OF VIBRIO PARAHEMOLYTICUS
Volety, A. K., F J. Genthner, W S. Fisher, S. A. McCarthy, AND K. Wiles. DIFFERENTIAL EFFECTS OF OYSTER (CRASSOSTREA VIRGINICA) DEFENSES ON CLINICAL AND ENVIRONMENTAL ISOLATES OF VIBRIO PARAHEMOLYTICUS. Presented at 91st Annual Meeting of the National Shellfisheries Association Annual Meeting, Halifax, Nova Scotia, 18-22 April 1999.
Three clinical (2030, 2062, and 2107) and three environmental (1094, 1163, and ATCC 17802) isolates of Vibrio parahaemolyticus were exposed to hemocytes and plasma collected from oysters (Crassostrea virginica) to determine their susceptibility to putative oyster defenses. Clinical strains were isolated from patients who became ill from the June 1998 food poisoning outbreak of V. parahaemolyticus associated with oysters harvested from Galveston Bay, Texas. Detection of thermolabile direct hemolysin (tlh) and thermostable direct hemolysin (tdh) genes in isolates was conducted using alkaline phosphatase- and digoxigenin-labeled probes. All isolates of V. parahaemolyticus possessed the tlh gene while only the clinical isolates had the tdh gene. Although pulse-field gel electrophoresis revealed that all clinical strains were identical, isolate 2062 was more susceptible to killing by oyster hemocytes than the other clinical isolates (2030, 2107). Overall, environmental isolates were more susceptible to hemocyte killing than clinical isolates. However, environmental isolates 1163 and ATCC 17802 had higher susceptibility to hemocyte killing than isolate 1094. When grown on nutrient agar plates, all strains displayed different colonial morphologies. Examination of cells of clinical isolates using electron microscopy did not reveal differences in degree of encapsulation. Bacterial susceptibility to hen egg white lysozyme and oyster plasma was investigated. Results indicate that while clinical strains are genetically identical, they may differentially express putative factors responsible for protection against killing by oyster hemocytes.