Disk diffusion tests for resistance to amoxicillin-clavulanic acid (amox-cla), imipenem, oxacillin, and ceftobiprole in S. aureus 2884 (A) and S. aureus 2884D (B). A 0.5 McFarland standard suspension was used as the inoculum for a 100-mm-diameter Mueller-Hinton agar plate upon which oxacillin (5 μg), amoxicillin-clavulanic acid (20/10 μg), cefoxitin (30 μg), ofloxacin (5 μg), and imipenem (10 μg) disks were placed as they would be for a routine disk diffusion test. Resistance to these antimicrobials was determined according to the guidelines of the CLSI and CASFM.