In vivo induction of resistance to macrolide antibiotics in staphylococci with erythromycin.

Abstract

In vivo induction of resistance to macrolide (Mac) antibiotics was investigated using mice infected with Staphylococcus aureus MS537 followed by treatment with either erythromycin (EM) or josamycin (JM). An EM-inducible strain MS537, in which only EM was an active inducer for Mac resistance, acquired in vivo resistance to both Mac antibiotics and lincomycin (LCM) 2 hr after an EM injection but the resistance of the induced cells was lost 2 days thereafter. Consequently, EM was found to have no therapeutic effect on MS537 infection and the number of resistant bacteria recovered from the kidney increased even after 6 intraperitoneal injections of 0.2 nig each of EM; the number of bacteria recovered from the kidney showing the same level as the controls without treatment. JM, one of the non-inducers for Mac resistance, by contrast, showed a therapeutic effect on MS537 infection and the number of organisms recovered from the kidney decreased to one-thousandth of that obtained with EM treatment, resulting in the survival of mice.