A 32-year-old man presents to the clinic with a painless ulcer on his penis that appeared two weeks ago. He reports unprotected sexual intercourse with multiple partners in the past month. He denies fever, rash, or systemic symptoms. On physical examination: Single, non-tender ulcer with clean edges and a firm base on the penile shaft (chancre). No lymphadenopathy. Serologic testing: Positive rapid plasma reagin (RPR) test with a titer of 1:32. Reactive treponemal antibody test, confirming primary syphilis. The patient is treated with the first-line antibiotic for syphilis, which is intramuscular Penicillin G Benzathine. What is the mechanism of action of this antibiotic?
