Studies on the effects of 3-acetyl-4"-isovaleryltylosin against multiple-drug resistant strains of Staphylococcus aureus.

The macrolide-resistance of multiple-drug resistant strains of Staphylococcus aureus was divided into two types; the decreased sensitivity of ribosomes (type I) and the decreased uptake (type II). Both types were resistant to erythromycin, tylosin and 3-acetyltylosin, and their resistance was not inducible. 3-Acetyl-4"-isovaleryltylosin inhibited the growth of both types. Protein synthesis on ribosomes of type I in vitro (S. aures MS-9610) was inhibited by 3-acetyl-4"-isovaleryltylosin, but little or no inhibition was seen with either tylosin or 3-acetyltylosin. Ribosomes of type II in vitro (S. aureus MS-8710) were sensitive to all macrolides. 3-Acetyl-4"-isovaleryltylosin accumulated about twice as much as 3-acetyltylosin in intact cell of type II.