An evaluation of three rapid coagglutination tests: Sero-STAT, Accu-Staph, and Staphyloslide, for differentiating Staphylococcus aureus from other species of staphylococci.

Three commercial coagglutination tests--Sero-STAT, Accu-Staph, and Staphyloslide--were performed in parallel with slide coagulase, tube coagulase, and thermostable nuclease tests on 100 methicillin-susceptible Staphylococcus aureus (MSS) strains, 100 methicillin-resistant S. aureus (MRS) strains, and 100 non-S. aureus staphylococcal strains (NSA). All three coagglutination tests showed sensitivities of 100% for MSS strains. For MRS strains, sensitivities were, respectively, 99%, 100%, and 99%. False-positive reactions were, respectively, 10%, 2%, and 2%. A marked difference in slide coagulase test sensitivity was found for MSS strains (79%) and MRS strains (14%). These findings suggest that the coagglutination tests may be less sensitive for detecting MRS strains than for detecting MSS strains and that these properties may be related to clumping factor reactivity. The high false-positive rate for Sero-STAT and even the 2% false-positive rate for Accu-Staph and Staphyloslide make clinical usefulness at this time somewhat problematic and debatable. In view of these findings, the authors prefer to retain the tube coagulase test and thermostable nuclease test for differentiation of S. aureus from non-S. aureus strains in their laboratory.