Photodynamic inactivation of Staphylococcus aureus by ecological antibacterial solutions associating LED (ʎ 450 ± 10 nm) with curcumin and olive leaf extracts.

Antimicrobial resistance is a problem in contemporary society, with Staphylococcus aureus standing out as a threat due to its ability to colonize, its pathogenicity, and its expression of several virulence factors. In this context, antimicrobial photodynamic inactivation (aPDI) emerges as an alternative to conventional microbicidal or microbiostatic systems, enabling numerous and successive applications without developing side effects and microbial resistance. In this context, an aPDI system against cultures of S. aureus based on a water-in-oil (W/O) emulsion incorporating curcumin as the photosensitizer (PS), with and without olive leaf extract (OLE), was developed and the antibacterial efficacy evaluated under LED activation (ʎ450 ± 10 nm) by depositing an energy density of 14 J/cm. The produced emulsified systems showed no significant differences in the droplet size and morphology, remaining stable along the tested period of 30 days. The bacterial reduction achieved after the first aPDI application for the emulsions added with curcumin and curcumin combined with the OLE was 5 log10 CFU.mL and 6 log10 CFU.mL, respectively, revealing a significant difference between the two groups (p < 0.0001). After the second aPDI application, an increased microbial reduction (7 log10 CFU.mL) was observed for both studied groups even with a low significant difference (p < 0.05). The PS loading through an emulsified system for aPDI obtained a bactericidal action against S. aureus, increased by applying two aPDI, showing a significant synergy between photodynamic inactivation, OLE delivery and antibacterial activity. In addition, the developed solutions were produced using natural products by an ecologically correct process.