EVALUATION OF PHOTODYNAMIC THERAPY USING METHYLENE BLUE COMBINED WITH AMIKACIN AGAINST BIOFILMS OF METHICILLIN-RESISTANT Staphylococcus aureus

Staphylococcus aureus is a Gram-positive bacteria capable of creating biofilms and also known for its presence in the clinical scenario. Biofilms make bacteria stronger and more resistant against antibiotics. Therefore, photodynamic therapy (PDT) is a promising method in which combined with a photosensitizer, for example methylene blue (MB) and antibiotics such as amikacin might show good results. The aim of this study was to evaluate whether the combined approach could enhance antimicrobial efficacy compared to either treatment alone. It was developed a 24h-biofilm of Methicillin-resistant Staphylococcus aureus (MRSA)) followed by the MB and the amikacin incubation for 15 minutes. Sequentially, they were exposed 50 J/cm² ( 660 nm, 37 mW/cm²). After that, the biofilm was mechanically detached for the serial dilution process, in which the concentrations of 10⁻⁴ and 10⁻⁶ were used for the drop plate technique performed on a Petri dish, where three drops of 100 μl each were plated on BHI agar and incubated for 24 hours for reading. Results demonstrated that the combination of PDT with methylene blue and amikacin significantly reduced the viability of MRSA. aureus biofilms. The most effective treatment against the MRSA strain was the combination of PDT with methylene blue and amikacin, presenting the lowest CFU/ml count. PDT with methylene blue and irradiated amikacin alone also showed significant reduction but were less effective than the combination. The control, LED, FS and AMC alone groups presented high counts, indicating low effectiveness indicating that the photodynamic mechanism is essential for optimal action. In conclusion, the study supports the use of PDT combined with antibiotics and a photosensitizer as a potential alternative strategy in treating biofilm-associated infections caused by MRSA. Further research is needed to optimize parameters such as light dosage, photosensitizer concentration, and exposure time for clinical applications. These findings are promising in antimicrobial resistance context and the need for innovative, non-invasive approaches.

This work was supported by FAPESP (2022/10251-0).