The effectiveness of antimicrobial photodynamic therapy with prodigiosin against reference strains of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa

Prodigiosin (PG) is a secondary metabolite of bacterial origin that is able to absorb the visible light and plays a role as a photosensitizer in photodynamic therapy (PDT). This in vitro study aimed to investigate the cytotoxicity of PG-mediated PDT against the reference strains of Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and Pseudomonas aeruginosa (P. aeruginosa). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of PG were determined. Each strain was then allocated into four groups as follows: G1: control (no treatment), G2: PG-treated groups that received different PG concentrations (1000-1.95 μM), G3: laser-treated group (wavelength: 520 nm, radiation dose: 187 J/cm²), and G4: PG-mediated PDT groups that were initially treated with different concentrations of PG and were then exposed to laser irradiation in the same way as the previous group. Finally, the number of colony-forming units per milliliter (CFU/mL) was calculated and analyzed using the SPSS software. PG had both bacteriostatic and bactericidal activities on the tested bacteria, with the maximum antibacterial effect being observed against S. aureus. In all bacterial strains, the maximum number of CFUs was observed in the control group followed by the laser-irradiated and PG-treated groups, but the differences were not statistically significant (p > 0.05). However, the utilization of PG-mediated PDT resulted in a significant decrease in the mean number of CFUs in all the tested bacteria (p < 0.0001). PG-mediated PDT had the potential to kill some bacterial strains in the laboratory. Yet, further studies are warranted to confirm its efficacy and safety to be applied in clinical settings.