Example of a disk diffusion test for inducible clindamycin resistance in a S. aureus. isolate. Inducible clindamycin resistance is indicated by the flattened border between the clindamycin disk (top right) and the erythromycin disk (top left), resulting in a characteristic 'D'-shaped area cleared of S. aureus. around the clindamycin disk. The two lower disks were included to test the isolate for penicillin (left) and oxacillin (right) resistance.