Comparison of several methods to determine methicillin-resistance in Staphylococcus aureus with focus on borderline strains

We compared the performance of several phenotypic tests to detect methicill in-resistant Staphylococcus aureus, with special focus on borderline strain s. The reliability of the agar screen oxacillin and BBL Crystal tests was a sserted for all methicillin-susceptible (n = 25), resistant (n = 29) and bo rderline beta-lactamase-hyperproducer (n = 10) strains. Whereas these tests failed to detect 4 of 5 rare borderline strains containing few cells with high-level methicillin resistance (i.e., a frequency of 10(-7)-10(-8)), a " two-temperature" disk diffusion method, performed simultaneously at 35 and 42 degrees C, detected all of such strains. (C) 2000 Elsevier Science Inc. All rights reserved.