Pristinamycin IIA is a macrolide antibiotic. It is a member of the streptogramin A group of antibiotics and one component of pristinamycin (the other being pristinamycin IA). It is produced by Streptomyces graminofaciens and other bacteria. (en)
Virginiamycin M1 is a macrocyclic lactone antibiotic that acts syngeristically with the structurally unrelated cyclic depsipeptides more commonly known as the virginiamycins B (ostreogrycin B or streptogramin B) and S to inhibit peptide elongation. This is achieved by blocking formation of a peptide bond between the growing peptide chain (peptidyl-tRNA) linked to the 50S ribosome and aminoacyl-tRNA. Virginiamycin M1 has proven to be highly active against Gram positive bacteria, particularly methicillin-resistant S. aureus. (en)