Lectin binding characteristics of the olfactory mucosa of channel catfish:Potential factors in attachment of Edwardsiella ictaluri

The olfactory organ is a primary infection sire for Edwardsiella ictaluri, the etiologic agent of enteric septicemia of channel catfish Ictalurus punc tatus. The olfactory mucosal surface is a major interface between host and pathogen where commonly occurring carbohydrates may act as receptors for ba cterial attachment. In this study, D-mannose, N-acetylgalactosamine, N-acet ylglucosamine, N-acetylneuraminic acid, D-galactose, and L-fucose were hist ochemically localized in the olfactory mucosa of channel catfish by using l ectins that preferentially bind these carbohydrates. These lectins were Con canavalin A (ConA), soybean agglutinin (SBA), pokeweed agglutinin (PWA), wh eat germ agglutinin (WGA), peanut agglutinin (PNA), and Ulex europaeus aggl utinin I (UEA-I), respectively. The olfactory mucosa expressed D-mannose ub iquitously, whereas L-Fucose and N-acetylneuraminic acid expression was spe cific to the apical mucosal surface. The carbohydrates D-galactose, N-acety lgalactosamine, and M-acetylglucosamine were most abundant in the sensory m ucosa, specifically olfactory receptor neurons and cells near the basal lam ina. Edwardsiella ictaluri was assayed for carbohydrate affinities by collo idal gold immunolocalization and transmission electron microscopy. Of the a nd-lectins examined, those against WGA and UEA-I cross-reacted most intense ly with Edwardsiella ictaluri, whereas cross-reactivities of anti-ConA, -SB A, and -PNA were more moderate. Double immunofluorescence labeling of exper imentally infected catfish showed E. ictaluri adherent to cell surfaces or intercellularly associated with labeled carbohydrate components of the olfa ctory mucosa. Preincubation of the olfactory mucosa with soluble D-galactos e significantly reduced bacterial adhesion compared with controls. Our resu lts indicate a specific pattern of carbohydrates present in the catfish olf actory mucosa and suggest carbohydrates participate in initial E. ictaluri attachment by acting as ligands for pathogen constituents.