The bacterial flora of the skin surface following routine MAL-PDT.

Photodynamic therapy using methylated 5-aminolevulate (MAL-PDT) appears to have an effect on non-neoplastic skin diseases, for example acne vulgaris and rosacea, for which antibiotics are sometimes used, and a possible antibiotic effect of PDT has previously been suggested. It does, however, also cause local immunosuppression and post-treatment barrier defects, which may promote infection. At the same time, PDT-induced therapeutic skin damage is sometimes confused with secondary bacterial infection by non-dermatologists. The possible changes in bacterial flora associated with MAL-PDT were therefore studied in 47 patients undergoing treatment. Skin swabs were taken immediately before applying the MAL and instantly after light irradiation. Bacterial growth was identified in 18 cases. No statistically significant changes were seen, either in the specific species found or the estimated bacterial density on the skin surface. The observations do not support the notion that routine MAL-PDT affects the bacterial flora of the skin in a clinically significant manner. Therefore, the possible antibacterial effect of routine MAL-PDT is probably not the main explanation of its apparent effect on non-neoplastic skin disease.