In situ adherence of Vibrio spp. to cryosections of Atlantic salmon, Salmosalar L., tissue.

Pathogenic and presumed non-pathogenic bacteria isolated from fish were tes ted for their adhesion to cryosections from different mucosal surfaces of A tlantic salmon, Salmo salar L. Adhered bacteria were detected by immunohist ochemistry. Mucus was stained and fixed with Alcian blue after incubation o f bacteria. The majority of the bacteria tested, i.e. Vibrio anguillarum se rotype O1, Vibrio salmonicida, Vibrio viscosus, Flexibacter maritimus and ' gut vibrios', i.e. Vibrio iliopiscarius and intestinal isolates of V. salmo nicida, all adhered to mucus on all salmon epithelial surfaces tested, incl uding sections from the foregut, hindgut, pyloric caeca, gills and skin. In contrast, V. anguillarum serotype O2, including both serotypes O2a and O2b , did not adhere to mucus, but did adhere to all other components of the ti ssues. As a positive control for adhesion of bacteria on cryosections, Esch erichia coli was bound to piglet ileal mucosal lining, and as a negative co ntrol for adhesion, Staphylococcus aureus was found not to bind to any of t he tissues tested. The present study shows that adhesion to mucus was not r estricted to pathogenic bacteria, and furthermore, that not all pathogenic bacteria studied adhered to mucus. Hence, on the basis of these findings, t he present authors suggest that V. anguillarum O2 may have an invasion stra tegy which does not involve adhesion to mucus, and thus, differs from the o ther pathogenic bacteria in the present study, which all bound to salmon mu cus.