Qualitative and quantitative changes in cutaneous bacteria associated with systemic isotretinoin therapy for acne conglobata.

Quantitative cultures in 40 patients treated with systemic isotretinoin demonstrated a significant reduction in the anaerobic diphtheroid, Propionibacterium acnes within one month of therapy and a continued suppression during 5 months of treatment. This reduction persisted after discontinuation of isotretinoin therapy despite a return of sebum excretion to pretreatment levels. Surface aerobic bacteria showed a significant reduction in the total number of organisms and significant qualitative changes. Gram negative bacteria were sharply reduced in both the anterior nares and skin while Staphylococcus aureus recovery increased significantly.