Effects of topical erythromycin on aerobic and anaerobic surface flora

The contents of acne lesions from 30 men with inflammatory acne vulgaris, obtained before and at the conclusion of 4 weeks of topical 2% erythromycin therapy, were cultured on aerobic and anaerobic plates. Sensitivity testing of cultures was performed with discs containing 50 mg erythromycin, in order to ascertain the prevalence of erythromycin-resistant strains of Propionibacterium acnes and aerobic micrococci. The percentages of patients in whom erythromycin-resistant micrococci could be isolated increased from 3 to 60% during topical erythromycin therapy, but no resistant P. acnes strains were isolated either before or after therapy. Considering the widespread use of topical antibiotics, long-term studies on their ecological effects are desirable.