RESPONSE OF PASTEURELLA-PISCICIDA AND FLEXIBACTER-MARITIMUS TO SKIN MUCUS OF MARINE FISH

The antibacterial activity present in the skin mucus of turbot Scophth almus maximus, seabream Sparus aurata and seabass Dicentrarchus labrax against Pasteurella piscicida and Flexibacter maritimus was evaluated . Using assays on agar plates, none of the mucus samples from the abov e fish showed any antibacterial activity against F. maritimus isolates . Turbot mucus inhibited the growth of the P. piscicida but mucus from seabream and seabass did not. Assays in liquid systems to determine t he survival of the above pathogens in the presence of skin mucus corro borated the results obtained by the agar plate method. The bactericida l properties of the mucus were lost after heat treatment at pH 3.5 and all skin mucus samples displayed activity against Staphylococcus aure us ATCC 25923, a strain resistant to lysozyme. These findings indicate d that thermolabile substances other than lysozyme were responsible fo r the antibacterial activity in mucus of marine fish. Enzymatic and he at treatments of the mucus also showed that factors other than complem ent were involved and that the active component(s) was likely a glycop rotein. Regardless of the source of isolation and degree of virulence, all P. piscicida and F. maritimus strains adhered strongly to the ski n mucus of the 3 fish species tested. Taking all of the foregoing resu lts into consideration, it appears that whereas a possible portal of e ntry for F. maritimus into the fish body is the skin, in P. piscicida another pathway must be involved.