Antimicrobial photodynamic therapy using sodium iron chlorophyllin against drug-resistant Cutibacterium acnes from patients with acne vulgaris

Antimicrobial resistance in Cutibacterium acnes is a growing concern, limiting treatment options for acne vulgaris (AV) and increasing the risk of opportunistic infections. Photodynamic therapy (PDT), using an effective photosensitizer (PS) and optimized light parameters, is a potent broad-spectrum antimicrobial strategy with minimal risk of resistance development. This study aimed to assess the efficacy of PDT using sodium iron chlorophyllin (CHL-Fe) as an in-house photosensitizer (CH-PDT) against 10 clinically isolated, drug-resistant C. acnes strains. The isolates, obtained from patients with mild to severe AV in a dermatology referral center, were resistant to one or more commonly prescribed antibiotics. CH-PDT was conducted using varying concentrations of CHL-Fe and red light (RL) fluences in laboratory conditions. A consistent bactericidal activity (> 3 log₁₀ CFU/mL reduction) was achieved across all resistance profiles with a fixed dose of CHL-Fe at 7.5 mg/dL combined with RL at 3.5 J/cm². Neither CHL-Fe nor RL alone, even at higher doses, produced similar results. The study included pan-, extensively, multi-, and single-drug-resistant strains, making the findings broadly applicable to clinical practice. These findings underscore CH-PDT as a promising nonantibiotic therapy for drug-resistant AV, with potential implications for eradicating C. acnes colonization and preventing infections in surgical and implant-related settings.