Antimicrobial effects of phototherapy and photochemotherapy in vivo and in vitro

Summary We investigated the antimicrobial effects of phototherapy and photochemotherapy in vivo and in vitro. First, Staphylococcus aureus samples were obtained using stamp agar medium from inflammatory lesions of 29 adult patients with atopic dermatitis before and after a single photochemotherapy. Therapy was oral PUVA (30 mg 8-methoxypsoralen, 8MOP plus 5 J/cm²UVA), topical PUVA (0·3% 8MOP plus 200mJ/cm²UVA) or UVB (80mJ/cm²) irradiation. The number of S. aureus on the lesions was significantly reduced, even after a single treatment with all therapies. Reductions (mean± SD) were 69·3 ± 26.9%, 76·3 ± 31·3% and 83·8 ± 18·5%. respectively. Secondly, we investigated the effect of PUVA (0·001% 8MOP plus 10, 20, 30, 40, or 50 mJ/cm²UVA) and UVB (10, 30, 50, or 100 mJ/cm²) irradiation on the proliferation of S. aureus in vitro. PUVA and UVB treatment markedly inhibited the proliferation in a dose-dependent manner. These results seem to indicate the possibility that the antimicrobial effect of UV radiation contributes to successful photochemotherapy in patients with atopic dermatitis.