Relationship between virulence factor genes in bovine Staphylococcus aureus subclinical mastitis isolates and binding to anti-adhesin antibodies.

Staphylococcus aureus is the most common aetiologic agent of contagious bovine mastitis. It is characterized by a wide array of virulence factors. The differences among strains jeopardize the development of effective vaccines against Staph. aureus mastitis. We tested the immunogenicity of a peptide subunit vaccine coding for three different adhesion factors, fibrinogen-binding protein (Efb), fibronectin-binding protein A (FnbpA) and clumping factor A (ClfA). Then we evaluated the influence of some virulence factors on the ability of specific anti-adhesin antibodies to react with sixteen Staph. aureus strains isolated from bovine subclinical mastitis. Immunization with the recombinant adhesins stimulated a strong humoural (IgG and IgA) and mucosal IgA immune response in all animals tested. Hyperimmune serum recognized with diverse efficiency the sixteen Staph. aureus strains and this circumstance correlated well with the level of expression of adhesins. Among the different virulence factors considered to classify strains, spa gene polymorphisms showed the strongest influence on isolate reactions to hyperimmune serum. Our results indicate the importance of a disease- and environment-specific analysis of isolates. Thus, as opposed to other pathogens to obtain an effective vaccine we should characterize multiple strains and identify the prevalent virulence factors expressed.