Antimicrobial photodynamic therapy with Ligularia fischeri against methicillin-resistant Staphylococcus aureus infection in Caenorhabditis elegans model

The high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infection threatens the effectiveness of current clinical settings. Antimicrobial photodynamic therapy (APDT) is a promising alternative to antibiotics for treating infections due to its low resistance. This study aimed to evaluate the antibacterial properties of APDT with L. fischeri extract (LFE) against MRSA and various skin and oral pathogens in vitro and its photopharmaceutical actions in Caenorhabditis elegans . The antimicrobial activities of APDT with LFE against pathogens were evaluated using plate counting method. The chemical profile was characterized using high-performance liquid chromatography and spectrophotometry. The growth rate assay, lifespan assay, and bacterial attachment on worms were performed to assess the therapeutics effects in C. elegans . The swab method was used for the detection of pathogens on the micropig skin surface. The APDT treatment with L. fischeri extract (LFE, 20 µg/mL) and red light (intensity of 120 W/m 2 ) reduced 4.3–4.9 log (colony forming unit/mL) of Staphylococcus aureus , MRSA, Cutibacterium acnes , Streptococcus mutans ; and 2.4 log (CFU/mL) of Candida albicans . Chemical analysis revealed that LFE enriched three active photosensitizers. APDT reduced bacterial populations on worms, recovered growth retardation, and improved lifespan in MRSA-infected C. elegans without causing severe side effects. The surface eradication of MRSA after exposure to LFE with red light was demonstrated on micropig skin. These findings highlight the significance of L. fischeri as a natural resource for the safe phototreatment of MRSA infection in the biomedical and cosmeceutical industries.