Virginiamycin complex contains two antibiotics, virginiamycin M1 and virginiamycin S1. Virginiamycin S1 is a macrolide antibiotic. It is a member of the streptogramin B group of antibiotics, which bind the 50S ribosomal subunit at the peptidyl transferase center to inhibit initiation and translocation. They show good bactericidal activity against methicillin-resistant S. aureus (MRSA), although resistance in MRSA is conferred by the cfr gene. Virginiamycin S1 acts synergistically with virginiamycin M1 to irreversibly inhibit protein synthesis in bacteria.
