Origin of Erythromycin-Resistant Strains of Micrococcus Pyogenes in Infections

Since the introduction of erythromycin in 1952 by McGuire and co-workers1and the first reports of its clinical application,* there has been increasing use of this antibiotic in the treatment of infectious diseases. It has been particularly effective in the treatment of infections caused by staphylococci which are resistant to penicillin and to other antibiotics.† Few strains of staphylococci isolated from infections shortly after the introduction of this antibiotic were found to be resistant to erythromycin in concentrations too great for clinical use.‡ According to Haight and Finland,9in 1952 all of 640 strains of staphylococci were sensitive to erythromycin in concentrations of 1.56γ/ml.; 96% were inhibited by 0.2 to 0.8γ/ml., and 87% were sensitive to 0.4γ/ml. Increased resistance to erythromycin occurs in vitro when strains of staphylococci are cultivated in increasing concentrations of erythromycin.§ Erythromycin-resistant strains of staphylococci have been found in the nasopharynges of hospital personnel