Surface Structure of Bacteroides nodosus in Relation to Virulence and Immunoprotection in Sheep

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Abstract
A comparative EM study was made of virulent ovine strains, benign ovine strains, bovine strains and culture variants of B. nodosus using negative staining, thin section and freeze-fracture etch techniques. The plasma membrane, peptidoglycan layer and outer membrane structures were similar in all the organisms; there were marked differences in the presence of pili, diffuse polar material and an additional layer. The variations in these surface structures were examined in relation to the virulence and immunoprotection against B. nodosus foot-rot in sheep. Only organisms with abundant pili caused virulent foot-rot; diffuse polar material and the additional layer may also be associated with virulence; conclusive evidence was lacking. Apparently, pili and .gtoreq. 1 unknown cell component, possibly diffuse polar material, but not the additional layer, were necessary for immunoprotection.