Evaluation of serotypes of Staphylococcus aureus strains used in the production of a bovine mastitis bacterin.

The five Staphylococcus aureus strains used in the manufacture of a commercially available bacterin were examined for capsular and surface polysaccharide serotypes. Double immunodiffusion assays of antigenic extracts of test and reference strains with monospecific typing sera to capsular serotypes 1, 2, 5, and 8 and to surface polysaccharide serotype 336 were performed to detect the specific reactivities and antigenic relationships of test samples. Antigenic extracts of two S. aureus strains reacted with antibodies to serotype 8, but not with antibodies to serotype 5, by producing specific precipitin lines. A third strain reacted with monospecific antibodies to serotype 5 and not with the antibodies to serotype 8. The extracts of two other strains failed to exhibit any detectable reaction with antiserum to serotypes 1, 2, 5, or 8. Antibodies to serotype 336, however, precipitated an identical, specific 336 antigen from the antigenic extracts of these two nontypeable strains. Thus, S. aureus bacterin includes one serotype 5, two serotype 8, and two serotype 336 strains, the three predominant serotypes responsible for bovine mastitis.