The effect of novel growth media on the virulence and toxicity of cellular and extracellular components of the fish pathogen Photobacterium damselae subsp. piscicida

Novel media for the preparation of antigens from the pathogen Photobacterium damselae subsp. piscicida were evaluated in respect to the promotion of synthesis of virulence factors. Certain formulations based on yeast extract and bacterial and / or fish peptone promoted the toxicity of ECPs and the virulence of bacterial cells administered via immersion or intraperitoneal injection. Crude capsular polysaccharide was proved to possess low toxicity. Heating of extracellular products abolished completely their toxicity, but freezing and PMSF treatment did not. Concentration of extracellular products using 12KD molecular weight cut-off dialysis membranes, influenced negatively the toxicity of extracellular products prepared in certain formulations.