TOXICITY OF THE EXTRACELLULAR PRODUCTS OF VIBRIO-DAMSELA ISOLATED FROM DISEASED FISH

In this work we analyzed the pathogenic in vivo and in vitro activitie s for both fish and mammals of extracellular products (ECP) of several isolates of Vibrio damsela implicated in disease problems in marine c ulture. The ECP from all the strains were strongly lethal for fish (LD 50 ranging from 0.06 to 3.7 mug protein/g fish) and mice (LD50 ranging from 0.02 to 0.43 mug protein/g mouse), causing death between 4 and 7 2 h after inoculation. These ECP samples possessed low proteolytic act ivity without production of caseinase, gelatinase, or elastase. Howeve r, most of them showed remarkable phospholipase and hemolytic activity for sheep, human, and turbot red blood cells. In addition, all the EC P samples were cytotoxic for fish and homoiothermic cell lines. The le vels of enzymic and cytotoxic activities were clearly associated with the degree of virulence for fish. Moreover, the enzymic patterns of bo th live cells and ECP evaluated with the API-ZYM system were very simi lar among the strains, indicative that most of the activities are asso ciated with exoenzymes. The in vivo and in vitro biological activities were considerably reduced after heat treatment (100-degrees-C for 10 min), but not totally lost in the highly virulent strains. Although we have demonstrated that the toxicity of the ECP is not directly associ ated with their lipopolysaccharides (LPS) content, these compounds cou ld confer some heat-stabilizing effect to the toxic fractions.