Efficacy of a latex agglutination test for rapid identification of Staphylococcus aureus: collaborative study

Fifteen laboratories completed a collaborative study comparing the efficacy of a latex agglutination kit (Aureus Test) with that of AOAC Official Method 987.09 (coagulase test for identification of Staphylococcus aureus). Each laboratory analyzed 240 strains of bacteria, including 160 isolates of S. aureus and 80 isolates of other bacteria. Upon receipt of cultures, collaborators subcultured each isolate on both tryptic soy agar (TSA) and Baird-Parker agar medium (BPA) to determine whether the growth medium has any effect on either method. For cultures grown on TSA, the latex test had sensitivity and specificity rates of 99.2 and 97.1%, respectively, whereas the coagulase test had respective rates of 98.4 and 92.5%. For cultures able to grow on BPA, the latex test had sensitivity and specificity rates of 99.2 and 96.6%, respectively, while the coagulase test had respective rates of 98.3 and 91.3%. By using the McNemar pairwise comparison test of the 2 methods, the false-positive and false-negative rates of the latex test were significantly lower (p < 0.01) than those of the coagulase test for strains grown either on TSA or BPA. The latex agglutination test for identification of S. aureus isolated from foods has been adopted by AOAC INTERNATIONAL.