KETOLIDES LACK INDUCIBILITY PROPERTIES OF MLSB RESISTANCE PHENOTYPE

Ketolides belong to a new class of semi-synthetic 14-membered-ring mac rolides, which differ from erythromycin A by having a 3-keto group ins tead of the neutral sugar L-cladinose. The ability of these molecules and their L-cladinose counterparts to induce MLSB resistance in staphy lococci (one strain) and streptococci (two strains) was investigated u sing a disc agar susceptibility method as well as measuring induction kinetics. All 14- and 15-membered ring macrolides tested showed induci ng activity. In contrast, ketolides were clearly unable to induce MLSB resistance, a result consistent with the high in-vitro activity of th is new class of antibiotics against erythromycin A-inducible resistant bacteria.