Evaluation of coagulase activity and protein A production for the identification of staphylococcus aureus

Abstract

The activities of coagulase and thermostable nuclease (TNase) and the production of protein A were studied in 338 bacterial strains. These included 213 isolates of Staphylococcus aureus to determine which characteristic was most specific for the identification of S. aureus. The evaluation of different protocols for interpretation of coagulase results was also undertaken. Protein A was analyzed by a sandwich enzyme-linked immunosorbent assay using microtiter plates coated with antiprotein A antibodies. Coagulase activities were determined according to the criteria recommended by Association of Official Analytical Chemists (AOAC; any degree of clot formation is a positive reaction), American Public Health Association (APHA; coagulase activities ≥ 3+ are positive reactions), and the Bacteriological Analytical Manual (BAM; only 4+ reaction is positive). It was found that the AOAC protocol, which had a test sensitivity of 97.7% and a specificity of 95.1% and could be completed within six hours, was more practical than the methods used by APHA and BAM. Compared with coagulase and TNase, protein A was a better marker of S. aureus; a high sensitivity (100%) and specificity (96.8%) were obtained by using protein A for the identification of S. aureus. Copyright © International Association of Milk, Food and Environmental Sanitarians.