Comparison of two commercially available test methods with conventional coagulase tests for identification of Staphylococcus aureus

The API STAPHase (Analytab Products, Inc., Plainview, N.Y.) and SeroSTAT Staph (Scott Laboratories, Fiskville, R.I.) tests were compared to the conventional tube coagulase test and a slide coagulase test by using fresh isolates of members of the family Micrococcaceae. The 4-h, 24-h, and combined readings of the tube coagulase test detected 94.5, 99.5 and 100%, respectively, of 219 Staphylococcus aureus isolates. The API STAPHase, SeroSTAT Staph, and slide coagulase tests detected 95.9, 95.4 and 95.9% of the isolates of S. aureus, respectively. There were no false-positive results with any of the systems when tested with 103 strains of members of the family Micrococcaceae other than S. aureus. We concluded that the STAPHase and SeroSTAT Staph tests were equal in accuracy to the slide coagulase and 4-h tube coagulase tests and were suitable for use in the clinical microbiology laboratory. However, SeroSTAT Staph gave faster results than the API STAPHase, and the test was easier to perform. Also, the false-negative rate was high enough with the STAPHase, SeroSTAT Staph, and the slide coagulase tests that all negative reactions should be confirmed with a tube test.