Effect of Flavobacterium psychrophilum strains and their metabolites on the oxidative activity of rainbow trout Oncorhynchus mykiss phagocytes

The oxidative activity of rainbow trout phagocytes was studied using a chem iluminescence technique using 12 different Flavobacterium psychrophilum str ains and their metabolites. Phagocytes were obtained from the head kidney o f rainbow trout Oncorhynchus mykiss. The addition of viable F. psychrophilu m or their metabolites to the phagocytes resulted in an immediate chemilumi nescence response. The stimulating effects of both the F. psychrophilum and their metabolites on the phagocytes were found to be heat stable. No signi ficant differences in stimulation capacity were found between the strains t ested. To investigate the nature of the stimulating agent, both the bacteri a and the supernatant were treated with either sodium metaperiodate or poly myxin B. Adding polymyxin B to the bacterial cells and supernatant did not change the chemiluminescence pattern, suggesting that the capacity of F. ps ychrophilum to stimulate the phagocytes probably is not due to Lipopolysacc harides (LPS). However, following incubation of the bacteria and their meta bolites with sodiun metaperiodate, the capacity to stimulate phagocytes was significantly impaired. This suggests that a carbohydrate component most l ikely plays an important role in the ability of F. psychrophilum to stimula te phagocytes. Opsonisation of the bacteria with native trout serum or with rabbit anti-F. psychrophilum serum resulted in an additional chemiluminesc ence peak which was significantly higher than the first peak. This extra pe ak disappeared following heat treatment of the trout serum and the rabbit a nti-F. psychrophilum serum, pointing towards the involvement of heat labile complement in opsonisation.