Comparison of the antimicrobial reduction effect of photodynamic inactivation with the addition of chlorophyll and curcumin photosensitizer in Aggregatibacter actinomycetemcomitans and Enterococcus faecalis [version 5; peer review: 1 approved, 3 approved with reservations]

Background Antibiotic resistance in oral pathogens such as Aggregatibacter actinomycetemcomitans and Enterococcus faecalis necessitates alternative antimicrobial strategies. Photodynamic inactivation (PDI) is a promising approach that utilizes a photosensitizer (PS), light, and oxygen to generate cytotoxic reactive oxygen species. This study evaluated the efficacy of two natural photosensitizers, curcumin and chlorophyll (from Medicago sativa L.), for the photodynamic inactivation of these bacteria. Methods Planktonic cultures of A. actinomycetemcomitans and E. faecalis were subjected to PDI using a 405 nm diode laser at various energy densities. The bacteria were treated with either curcumin (1.6 mg/mL) or chlorophyll (1.6 mg/mL) prior to laser irradiation. Bacterial viability was assessed using the colony-forming unit (CFU) assay. Groups without PS and without light served as controls. Results At an energy density of 1.59 J/cm2, laser irradiation resulted in a reduction of 35.8% and 36.7% for A. actinomycetemcomitans and E. faecalis, respectively. The addition of chlorophyll significantly enhanced bacterial reduction to 64.4% and 69.3%. Curcumin demonstrated superior efficacy, achieving bacterial reduction of 89.8% and 89.4% for A. actinomycetemcomitans and E. faecalis, respectively. The differences between the PS groups and the control groups were statistically significant (p < 0.05). Conclusions Curcumin is a significantly more effective natural photosensitizer than chlorophyll from Medicago sativa L. for the photodynamic inactivation of A. actinomycetemcomitans and E. faecalis. These findings point to the prospect of curcumin-based PDI as a potent therapeutic alternative for combating resistant oral infections.