Evaluation of a Latex Agglutination Test for Rapid Identification of Staphylococcus aureus from Foods

A latex agglutination kit (AUREUS TEST™) for the rapid identification of Staphylococcus aureus was evaluated in this study. The reagent consists of polystyrene latex particles sensitized with rabbit anti-protein A immunoglobulin G and fibrinogen. Due to the respective binding of bacterial protein A with immunoglobulin G and coagulase with fibrinogen, an agglutination reaction occurs within 1 min when the latex is mixed with a suspension of S. aureus. Of 157 S. aureus isolates (138 from foods) and 110 non-S. aureus isolates (58 species belonging to 19 genera), the sensitivity and specificity of the latex test were 100 and 94.4–100%, respectively. The results were comparable to the conventional coagulase test. Therefore, it is proposed that suspicious colonies of S. aureus on Baird-Parker agar medium be subcultured to tryptic soy agar for overnight incubation. Cultures grown on tryptic soy agar are used for latex agglutination test. The latex agglutination test can be finished within minutes and could be used as an alternative rapid procedure of the coagulase test, which needs several hours or even overnight incubation for completion. In addition, all S. aureus isolates grown on Baird-Parker agar also could be correctly identified by the latex reagent.