Review Question - QID 108553

A 36-year-old man working as a hospital technician presents with a four day history of a leg laceration after tripping on the sidewalk in the city. On presentation, a pustule on the lower leg is observed as seen in Figure A. He complains of pain on ambulation and palpation. A culture grows gram-positive cocci. After a failed trial of nafcillin, he is started on another antibiotic. Ten minutes after an infusion of the new antibiotic, he develops flushing and an erythematous rash on his face and trunk. What is the mechanism of resistance to the antibiotic most likely administered in this case?