Question

A 32-year-old woman presents to the ambulatory care clinic with a painful, fluctuant soft tissue mass on her left thigh that has been enlarging over the past four days. She has no significant past medical history. Vital signs are within normal limits. An incision and drainage are performed, yielding purulent material that is sent for microbiologic analysis. Two days later, the culture grows *Staphylococcus aureus*. Antimicrobial susceptibility testing reveals resistance to oxacillin and erythromycin, but the isolate is initially reported as susceptible to clindamycin. The laboratory performs an additional disk diffusion assay by placing the erythromycin and clindamycin disks adjacent to each other on the agar plate. A distinct flattening of the clindamycin zone of inhibition adjacent to the erythromycin disk is observed. Based on these laboratory findings, the physician decides to prescribe an alternative oral antibiotic instead of clindamycin. Which of the following best describes the molecular mechanism responsible for the phenomenon observed in the adjacent disk diffusion testing?