Select plates containing 20-200
colonies, unless only plates at lower dilutions (>200 colonies) have colonies with
typical appearance of S. aureus. Colonies of S. aureus are circular, smooth,
convex, moist, 2-3 mm in diameter on uncrowded plates, gray to jet-black,
frequently with light-colored (off-white) margin, surrounded by opaque zone and
frequently with an outer clear zone; colonies have buttery to gummy consistency
when touched with inoculating needle.