Evaluation of latex agglutination and microtube coagulase tests for detection of Staphylococcus aureus

In a blind study, a latex agglutination test (Serostat Staphylococcus, Scott Laboratories) and a microtube coagulase test (Staphase, API) were evaluated for their ability to detect Staphylococcus aureus. Of 289 isolates of catalase-positive, gram-positive cocci, 122 were identified as S. aureus based on positive reactions in at least three of the following tests: tube coagulase, slide coagulase, DNase production, or anaerobic fermentation of mannitol. The latex agglutination test gave positive reactions for all S. aureus isolates and 10 (6%) non-S. aureus isolates. The slide coagulase test was positive for 121 S. aureus isolates and three (2%) non-S. aureus isolates. The microtube coagulase test detected 53, 90, and 98% of the S. aureus isolates after 2, 4, and 24 hr, respectively. In contrast, the conventional tube coagulase test detected 97% of the S. aureus isolates after 2 hr, and 98% after 4 and 24 hr. Two isolates of S. aureus gave negative tube coagulase reactions at 37 degrees C, but positive reactions at room temperature after 24 hr. The combination of tube and slide coagulase tests provided the most reliable results. The slide and tube coagulase tests gave more reliable results than the latex agglutination and microtube coagulase tests, respectively.