Abstract
According to an epidemiological survey of drug resistance in Staphylococcus aureus, it was found that there are three types of cross-resistance to macrolide antibiotics (EM, erythromycin: OM, oleandomycin: LM, leucomycin: SP, spiramycin), i. e., resistance to EM, OM, LM, and SP, to EM and OM, and inducible resistance to "EM, OM" In the inducible strains of S. aureus, EM and OM are active inducers, and the optimal concentrations of the inducers are 0.1μg/ml and 1.0 μg/ml, respectively. The induction of high resistance (800 μg/ml or more) to both EM and OM occurred within 10min exposure to 0.1μg/ml of EM, and the resistance of induced cells was lost after overnight growth in the absence of inducer. After 1 to 3hr exposure to 1.0μg/ml of OM, the inducible strains acquired high resistance (100μg/ml or more) to EM and to a lesser extent, resistance to OM, and the acquired resistance was lost when grown in antibiotic free media. When a known concentration of EM was mixed with the induced cells or with a crude extract from induced cells which had acquired high resistance to EM and OM, the antibiotic activity of EM was still retained in the mixture, indicating that the induced mixture or the extract from the induced cells was incapable of antibiotic (EM) inactivation under the test conditions.
