Virginiamycin M1 is a macrolide antibiotic that reversibly inhibits protein synthesis [1][2][3].

Virginiamycin complex contains two antibiotics, virginiamycin M1 and virginiamycin S1. Streptogramins are divided into class A and class B based on their structures. Virginiamycin M1, also known as Streptogramin A, is a member of the streptogramin A 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 M1 has activity against gram-positive and in select cases gram-negative bacteria. Combination of group A and B streptogramins exhibit bactericidal activity [1]. Virginiamycin M1 acted synergistically with virginiamycin S1 to irreversibly inhibit protein synthesis in bacteria. In cell-free systems, Virginiamycin M1 and virginiamycin S1 bound to the large ribosomal subunit, and the affinity of ribosomes for VS is increased by VM [2][3].

References:
[1].  Fair RJ, Tor Y. Antibiotics and bacterial resistance in the 21st century. Perspect Medicin Chem. 2014 Aug 28;6:25-64.
[2].  Kehrenberg C, Cuny C, Strommenger B, et al. Methicillin-resistant and -susceptible Staphylococcus aureus strains of clonal lineages ST398 and ST9 from swine carry the multidrug resistance gene cfr. Antimicrob Agents Chemother. 2009 Feb;53(2):779-81.
[3].  Parfait R, Cocito C. Lasting damage to bacterial ribosomes by reversibly bound virginiamycin M. Proc Natl Acad Sci U S A. 1980 Sep;77(9):5492-6.