Pathogenesis of Experimental Vibriosis in Larval American Oysters, Crassostrea virginica

Larval oysters were experimentally infected with isolates of pure cultures of marine Vibrio sp. These animals were studied live, histologically, with the immunofluorescent test and with electron microscopy. All inoculated groups, but no control groups, demonstrated decreased growth and/or high mortality.One bacterial isolate attached preferentially to larval shell and destroyed mantle tissue as it grew along the internal surface of the shell. Phagocytes consumed invading bacterial cells but were ultimately overwhelmed by the infection.The second bacterial isolate caused velar damage in young larvae that remained active. In these larvae, the velar cells became detached or internally disorganized and lost their rectractor muscle insertions. In more advanced larvae, detachment of absorptive cells of the digestive gland was the earliest change observed and seemed to result from attachment of bacterial antigens to the cell surface. In both younger and more advanced larvae, food cycling and nutrient utilization...