A 13-Year-Old Boy Is Brought to the Emergency Department Due

A 13-year-old boy is brought to the emergency department due to a skin swelling.  Temperature is 38.4 C (101.1 F) .  Physical examination shows an area of erythema, warmth, and tenderness on his right distal leg.  Laboratory results are notable for leukocytosis. He has a recurrent history of skin infection.  The patient is started on intravenous nafcillin.  Three days later, his symptoms haven't improved.  A pus culture is obtained and shows gram-positive cocci in clusters, and sensitivity testing showed resistent to nafcillin but sensitive to vancomycin.  Which of the following is the most likely explanation for nafcillin treatment failure in this patient?

A) Active drug transport out of the cell
B) Enzymatic degradation of the drug
C) Mutation in DNA gyrase
D) Mutation in RNA polymerase
E) Poor interaction with binding proteins