Role of the S-layer proteins of Campylobacter fetus in serum-resistance and antigenic variation: a model of bacterial pathogenesis.

Campylobacter fetus are microaerophilic gram-negative bacteria that are pathogens of animals and humans. These organisms possess paracrystalline surface (S-) layers, composed of acidic high molecular weight proteins. C. fetus strains possessing S-layers are resistant to C3b binding, which explains both serum and phagocytosis-resistance. C. fetus strains also can vary the subunit protein size, crystalline structure, and antigenicity of the S-layer it expresses. Therefore, its S-layer permits C. fetus to resist complement and antibodies, two of the key defenses against extracellular pathogens. C. fetus possesses several full-length genes encoding S-layer proteins with both conserved and divergent sequences, which permits gene rearrangement and antigenic variation.