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 psychrophilum recovered from a case of necrotic myositis affecting rainbow trout 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. Furthermore, the CEP did not degrade furanacryloyl-L-leucylglycyl-L-prolyl-alanine (FAT-GPA), chondroitin sulphates A, B or C, heparan sulphate, keratan sulphate, hyaluronic acid, elastin or rainbow trout erythrocytes. The addition of the protease inhibitors 1,10-phenanthroline, ethylenediamine-tetraacetic acid (EDTA) and EGTA to the CEP halted its ability to degrade gelatin in vitro and to produce muscle necrosis in rainbow trout in vivo. In vitro and in vivo activity was restored following the addition of 1 mM zinc chloride 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 pathogenesis of necrotic myositis in rainbow trout.