PRODUCTION OF PUTATIVE VIRULENCE FACTORS BY RENIBACTERIUM-SALMONINARUM GROWN IN CELL-CULTURE

A cell culture system, employing the fish cell line Epithelioma papill osum cyprini (EPC), was developed to study the synthesis of intracellu lar antigen and the expression of putative virulence factors by Reniba cterium salmoninarum. EPC cultures infected with R. salmoninarum could be maintained for 7 weeks, during which the pathogen multiplied intra cellularly. Immunohistochemical examination of infected cultures revea led the production of the p57 antigen, haemolysin and cytolysin. The i ntracellular nature of the infection was confirmed by transmission ele ctron microscopic examination of EPC monolayers. A comparison of the r elative virulence of bacterial cells cultured in EPC cells and on agar plates revealed that the former were markedly more virulent in challe nge experiments with juvenile rainbow trout (Oncorhynchus mykiss Walba um). The EPC cell culture model provided a system for the study of R. salmoninarum under more natural conditions than those achieved with pl ate culture techniques.