A 64-year-old woman with poorly controlled type 2 diabetes mellitus presents to the emergency department with a 1-week history of progressive erythema, warmth, and swelling of her left thigh. She reports a small cut from gardening 10 days ago. Vital signs show temperature 38.9°C, heart rate 102/min, and blood pressure 128/76 mmHg. On examination, there is a 3- × 4-cm fluctuant, tender mass with surrounding cellulitis on the medial thigh. An abscess is drained, and fluid culture grows gram-positive cocci arranged in clusters that are coagulase-positive and resistant to oxacillin on disk diffusion testing. Which of the following best explains this organism's resistance to oxacillin and other penicillinase-resistant beta-lactams?

1. A)Production of a beta-lactamase enzyme that hydrolyzes the beta-lactam ring of oxacillin
2. B)Decreased permeability of the cell wall to oxacillin due to altered lipopolysaccharide composition
3. C)Active efflux of oxacillin via energy-dependent membrane pumps
4. D)Acquisition of an altered penicillin-binding protein (PBP2a) encoded by the mecA gene with reduced affinity for beta-lactamsGABARITO
5. E)Enzymatic acetylation of the amino group on the oxacillin molecule, rendering it inactive