Evaluation of three Staphylococcus aureus proteins involved in the adhesion process as antigens for the detection of bovine intramammary infections

Abstract

Introduction. Fast and accurate diagnosis is one of the key strategies in the successful control of intramammary infections caused by Staphylococcus aureus . Immunoassays are one of the diagnostic tools that have been proposed for the detection of S. aureus infection because they offer an advantage in terms of cost and are fast and easy to use compared to other diagnostic tests. Gap statement. The main challenge of the immunoassays is to identify antigens or serological markers that allow accurate discrimination between infected and uninfected cows with S. aureus , since this bacterium can naturally colonize different areas of the animal body. Aim. To evaluate three S. aureus proteins (IsdA, ClfA, SdrD) involved in the adhesion process as antigens to detect indicator antibodies of bovine intramammary infections. Methodology. Ninety-six cows in lactation and not vaccinated against S. aureus were included. Forty-eight of these cows were infected with S. aureus , while the rest (n=48 cows) were uninfected. Blood and milk samples were collected from each animal to recover serum and whey. IgG titres against the three proteins individually and combined (Mix) were measured in each sample using an enzyme-linked immunosorbent assay (ELISA) test. Results. Significant differences in the IgG response against the proteins evaluated were observed, highlighting the antigenic potential of IsdA and demonstrating that some antigens can detect specific antibodies of infection better than others. According to receiver operating characteristic (ROC) curve analysis, the combined proteins showed the most remarkable capacity (sensitivity of 79 % and specificity of 77 %) to differentiate between infected and uninfected cows when blood samples were used. In addition, the combined proteins also showed the highest specificity (94 %) when using milk samples. Conclusion. Our findings provide information on the usefulness of three adhesion-associated S. aureus proteins in detecting serological markers of intramammary infections in bovines.