Few studies evaluating susceptibility testing of methicillin-resistant staphylococci have included isolates of Siaphylococcus epidermnidis, a known pathogen in many types of serious infections. We tested 175 S. epidermidis and 95 Staphylococcus aureus isolates to determine the most sensitive procedures for detecting methicillinresistant staphylococci. Reference procedures included agar dilution with methicillin and 4% NaCl in the agar and broth microdilution with methicillin and 2% NaCI in cation-supplemented Mueller-Hinton broth. After 24 h of incubation, the results from both methods correlated well and were within 1 log2 dilution for all isolates tested. Only one-half of all resistant isolates (92 of 183) were detected at 18 h by using the standard disk diffusion technique with 5-,ig methicillin disks, and even fewer were detected with 10-,lg methicillin disks and newly recommended zone-size criteria. However, the standard disk diffusion method with 4% NaCl in the agar increased the sensitivity and specificity for identification of the proper phenotype to greater than 92%. The spread plate aild new spot techniques, both using agar with 4% NaCl, were also sensitive methods. Of 47 S. epidermidis isolates tested against oxacillin, 6 (13%) were oxacillin susceptible but methicillin resistant. Two automated systems, the Automicrobic system (Vitek Systems) and MicroScan (American MicroScan), as well as two broth screening systems available from Remel and Austin Biological Laboratories, failed to detect several resistant isolates, depending on the species.

-positive isolates phenotypically susceptible to cefoxitin (-methicillin-sensitive [MSSA]) have been identified. We describe the treatment and outcomes among patients with-MSSA bloodstream infections (BSI) and MRSA BSI matched 1:1 for age, BSI origin, and BSI type ( = 17 per group). Compared to MRSA BSI patients, -MSSA BSI patients more often experienced clinical failure (58.8% and 11.8%, = 0.010), driven largely by persistent bacteremia (35.3% and 11.8%). -MSSA BSI patients may be at higher risk for poor clinical outcomes.