Studies on the Mode of Action of the Streptogramin Antibiotics

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Abstract
Streptogramin is a complex antibiotic containing 2 components, streptogramin A and streptogramin B. The individual components are bacteriostatic whereas the mixture is bactericidal. At growth-limiting concentrations streptogramin A and the streptogramin complex inhibit Staphylococcus aureus by blocking protein synthesis but not nucleic acid and cell wall synthesis. Protein, nucleic acid and cell wall synthesis were all reduced in the presence of streptogramin B. Streptogramin A, but not streptogramin B, inhibits the binding of radioactive chloramphenical to bacterial ribosomes. However, streptogramin B enhances this effect of streptogramin A in a cell-free system containing both bacterial soluble fraction and ribosomes. The results suggest that streptogramin A inhibits protein synthesis by bacteria at the ribosome level, and that this effect is enhanced by streptogramin B.