Necrotic myositis of rainbow trout, Oncorhynchus mykiss (Walbaum): proteolytic characteristics of a crude extracellular preparation from Flavobacterium psychrophilum

A crude extracellular preparation (CEP) from a strain of Flavobacterium psy chrophilum recovered from a case of necrotic myositis affecting rainbow tro ut was capable of causing severe,muscle necrosis in rainbow trout following intramuscular injection. Cell wall-associated preparations, however, were unable to produce similar lesions in experimentally injected fish. The CEP degraded gelatin and type II collagen but not type I or type IV collagen. F urthermore, the CEP did not degrade furanacryloyl-L-leucylglycyl-L-prolyl-a lanine (FAT-GPA), chondroitin sulphates A, B or C, heparan sulphate, kerata n sulphate, hyaluronic acid, elastin or rainbow trout erythrocytes. The add ition of the protease inhibitors 1,10-phenanthroline, ethylenediamine-tetra acetic acid (EDTA) and EGTA to the CEP halted its ability to degrade gelati n in vitro and to produce muscle necrosis in rainbow trout in vivo. In vitr o and in vivo activity was restored following the addition of 1 mM zinc chl oride to the protease inhibitor-treated CEP, suggesting that this strain of F. psychrophilum secretes a protein complex with zinc metalloprotease-like activity. This protein complex, therefore, appears to be involved in the p athogenesis of necrotic myositis in rainbow trout.