Photodynamic inactivation and its effects on the heterogeneity of bacterial resistance

Antimicrobial resistance is a growing threat to global public health, requiring innovative approaches for its control. Photodynamic inactivation (PDI) with light-activated photosensitizers has emerged as a strategy to combat resistant bacteria, challenging the intrinsic heterogeneity of bacterial populations. This study evaluates the impact of PDI on both heterogeneity and shape of the distribution profile of resistant bacterial populations, specifically on strains of Staphylococcus aureus resistant to amoxicillin, erythromycin, and gentamicin, for exploring its potential as an adjuvant therapy in the fight against bacterial resistance. Curcumin (10 µM) was used as a photosensitizer and five cycles of PDI were applied on Staphylococcus aureus strains under 450 nm irradiation of 10 J/cm² energy density. The resistance variations amongst bacterial subpopulations were investigated by calculating the minimum inhibitory concentration (MIC) before and after PDI treatment. MIC was significantly reduced by the antibiotics tested post-PDI and a reduction in the heterogeneity of bacterial populations was recorded, suggesting PDI can effectively decrease the resistance diversity of Staphylococcus aureus. The result reinforces the potential of PDI as a valuable adjuvant therapy, offering a promising avenue for mitigating bacterial resistance and promoting more effective treatment strategies against resistant infections.