INHIBITION OF THE ATTACHMENT OF FLAVOBACTERIUM-BRANCHIOPHILUM TO THE GILLS OF RAINBOW-TROUT, ONCORHYNCHUS-MYKISS (WALBAUM)

Preliminary experiments are described which aimed to identify compound s that could inhibit the attachment of Flavobacterium branchiophilum s trains LAB4a and ATCC 35035 to the gills of rainbow trout. Total inhib ition was never achieved, regardless of the compound tested. Formalin- killed or acetone-killed F. branchiaphilum cells retained at least som e of their adherent nature, relative to untreated (live) cells. Adhere nce was reduced by 22-33% following immersion of fish in one lit re of water containing 0.21 mg of a homologous crude fimbrial extract. When fish were immersed in water containing hyperimmune rainbow trout anti -LAB4a serum, a dose-dependent decrease in attachment (a reduction of 15% to 63%) of LAB4a to the gills was observed. Rainbow trout anti-LAB 4a serum also reduced the attachment of ATCC 35035 to the gills, but t his reduction was not significant. Adherence of LAB4a was not inhibite d following exposure of fish to group 1 carbohydrates (arabinose, mann ose and xylose), group 2 carbohydrates (dextrose, galactose and lactos e), group 3 carbohydrates (galactosamine, glucosamine and fucose) or g roup 4 carbohydrates (N-acetyl-D-glucosamine, N-acetyl-D-galactosamine , N-acetylneuraminic acid and the globoceramide glycolipid from human erythrocytes). In contrast, when rainbow trout erythrocytes were incub ated with the bacteria prior to bath challenge, this resulted in an 87 % and 53% reduction in gill-associated LAB4a and ATCC 35035 antigen, r espectively, following immersion of rainbow trout in this suspension.