INHIBITION OF TRANSLATION AND 50S-RIBOSOMAL-SUBUNIT FORMATION IN STAPHYLOCOCCUS-AUREUS CELLS BY 11 DIFFERENT KETOLIDE ANTIBIOTICS

Eleven structurally similar ketolide antibiotics were tested at a conc entration of 1 mu g/ml for their relative inhibitory effects on growth and ribosome activities in Staphylococcus aureus cells. Ten of the co mpounds examined had an inhibitory effect on protein synthesis at this concentration and eight of the 11 compounds were also effective inhib itors of the formation of the 50S ribosomal subunit. All of the drugs tested inhibited protein synthesis to a greater extent than they affec ted 50S subunit formation. The decline in growth rate and cell number was proportional to the effect on ribosome formation and function. The growth of an ermC erythromycin-resistant strain of S. aureus was also significantly inhibited by nine ketolide compounds, suggesting that t hey were not inducers of methylase gene expression. These inhibitory a ctivities can be related to structural differences between these ketol ide antibiotics.