Antimicrobial susceptibility of photodynamic therapy (UVA/riboflavin) against Staphylococcus aureus

Purpose: To assess S. aureus in vitro viability after the exposure to ultraviolet light A (UVA) and riboflavin (B2). Methods: Samples of S. aureus in 96 well plates (in triplicate) were exposed to riboflavin (B2) and ultraviolet light A (365 nm wavelength) at a power density of 3 mW/cm2, 8 mm spot diameter, for 30 minutes. Control groups were prepared as well in triplicate: blank control, ultraviolet light A only, riboflavin only and dead bacteria Control. The bacterial viability was measured using fluorescent microscopy. In order to investigate the occurrence of "viable but non-culturable" microorganisms after treatment, the cell viability was also investigated by plate culture procedure onto a broth medium. Statistical analysis was performed using the triplicate values from each experimental condition. Results: No difference was observed among the treatment group and the control samples (p=1). Conclusion: The combination of riboflavin 0.1% and ultraviolet light A at 365 nm did not exhibit antimicrobial activity against oxacillin susceptible S. aureus.