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Gramicidin
Pristinamycin
Quinupristin/dalfopristin
Virginiamycin

Streptogramins

Streptogramin antibiotics are costituted by couples of compounds that act in sinergy and are produced by various species of Streptomyces. One of these compounds, virginiamycin, has been extensively used as a growth promoter in animal husbandry. Another streptogramin, pristinamycin, is sometimes used as an antistaphylococcal agent, but plasma concentrations after oral administration are limited and solubility problems make parenteral use quite challenging. A formulation consisting of the water-soluble derivatives, quinupristin and dalfopristin, is suitable for infusion and is now used for human therapy.

This class of antibiotics includes: Pristinamycin, Quinupristin/dalfopristin, Virginiamycin.

The two components of streptogramin antibiotics are structurally different. Alone they exhibit very weak bacteristatic activity, but in combination the effect is bactericidal. Component A is a polyunsaturated peptolid that causes distortion of the aminoacyl-tRNA binding site, hindering further growth of the peptide chain. The action of component B, a hexadepsipeptide, is less well understood, but it hypothesized that it binds to an adjacent site and that the combined effect is to obstruct the channel through which the nascent peptide is extruded from the ribosome. Protein synthesis is completely blocked and the consequences are lethal to the bacterial cell.

The activity of streptogramins is restricted to Gram-positives. Their major feature is that they show activity against multiresistant staphylococci (MRSA) and some enterococci (VRE), notably Enterococcus faecium. Unfortunately, E. faecalis, which is more commonly encountered, is often resistant.

 


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