Evidence of Resistance Development by Staphylococcus aureus to an In Vitro , Multiple Stage Application of 405 nm Light from a Supraluminous Diode Array

OBJECTIVE: The aim of this study was to determine whether Staphylococcus aureus could develop a resistance to 405 nm light. BACKGROUND DATA: Research indicates that certain wavelengths and treatment parameters of light promote growth of bacteria; however, our earlier work indicated that blue light effectively inactivates growth of S. aureus in vitro. METHODS: S. aureus was tested because of its frequent isolation from skin infections and wounds. The organism was treated with 405 nm light from supraluminous diodes at a dose of 9 J/cm(2). RESULTS: As anticipated, blue light produced a significant (p≤0.05) inactivation of S. aureus growth. Subsequent applications of blue light to subcultured generations of S. aureus were increasingly effective through four stages (generations). Beginning with stage five, a decrease in effectiveness (resistance) was observed. CONCLUSIONS: Appropriate doses of 405-nm blue light inhibit the growth of S. aureus in vitro. This research does suggest that S. aureus may be capable of developing resistance to blue light irradiation.