PROTEINS FOUND WITHIN PORCINE RESPIRATORY-TRACT SECRETIONS BIND LIPOPOLYSACCHARIDES OF ACTINOBACILLUS-PLEUROPNEUMONIAE

Affinity for porcine respiratory tract secretions was found in some is olates of Actinobacillus pleuropneumoniae and involved lipopolysacchar ides (LPS) (M. Belanger, S. Rioux, B. Foiry, and M. Jacques, PEMS Micr obiol. Lett. 97:119-126, 1992). In the present study, the affinity for a crude preparation of porcine respiratory tract mucus of isolates of the Pasfeurellaceae family, i.e., Actinobacillus, Haemophilus, and Pa steurella spp., and of some unrelated gram-negative bacteria was exami ned. Affinity for crude porcine respiratory tract mucus was not a prop erty shared by all Pasteurellaceae isolates tested. Furthermore, affin ity for the porcine crude mucus preparation mas not unique to the Past eurellaceae group and did not seem to be restricted to bacteria origin ating from pigs. Different surface properties of A. pleuropneunaniae i solates in relation to their adherence to crude mucus were examined. T he capsular layer seemed to mask the adhesin and interfered with adher ence to crude mucus. Two poorly capsulated isolates, which had a more hydrophobic surface and bound Congo red, were also heavily labeled by gold particles coated with polymyxin, which is known to interact with the lipid A-core region of LPS, and adhered strongly to respiratory tr act secretions. Tetramethylurea, charged polymers, divalent cations, c helators, monosaccharides and amino sugars, or lectins were unable to inhibit adherence of A. pleuropneumoniae to the crude mucus preparatio n. To identify the receptor(s) recognized by the lipopolysaccharidic a dhesin of A. pleuropneumoniae, affinity chromatography was used. Two b onds, which were proteinaceous in nature, of 10 and 11 kDa were recove red. Our results suggest that two low-molecular-mass proteins present in porcine respiratory tract secretions bind A. pleuropneumonia LPS.