Virginiamycin S1 is one of a family of depsipeptide antibiotics co-produced with ostreogrycin A and used as a synergistic mixture. Virginiamycin S1, also known as Staphylomycin S and Factor S among other synonyms, was discovered independently and named by several groups, leading to considerable confusion in the literature. Virginiamycin S1 acts a synergist, binding to the conformational change of the peptidyl transferase centre of the 50S ribosome induced by ostreogrycin A. Virginiamycin S1 differs from virginiamycin B in lacking the dimethylamino moiety on the phenyl ring.