• antimicrobial photodynamic therapy;
  • comet assay;
  • cutaneous microorganisms;
  • DNA damage;
  • genotoxicity;
  • keratinocytes;
  • methylene blue;
  • safety

SummaryBackground Work has shown that cutaneous microbial species associated with skin conditions of microbial aetiology are susceptible to killing by antimicrobial photodynamic therapy (APDT) using visible light and methylene blue.

Objectives To evaluate immediate and delayed genotoxicity of APDT on keratinocytes in vitro.

Methods A combination of methylene blue (100 µg mL−1) and visible light (42 mW cm−2), as used in studies of microbe and keratinocyte cytotoxicity, was employed to test a human keratinocyte cell line (H103) for genotoxic damage by comet assay.

Results The comet assay was able to detect genotoxic damage in H2O2-treated keratinocytes (positive control). APDT did not cause either immediate or delayed genotoxic damage in keratinocytes following APDT of up to 180 min.

Conclusions APDT sufficient to reduce microbes by seven log cycles showed no detectable genotoxic effects on keratinocytes. APDT applied in vivo may represent a useful low-risk alternative to conventional antimicrobial treatment in dermatology.