Blue 470-nm Light Kills Methicillin-Resistant Staphylococcus aureus (MRSA) in Vitro

Abstract

Background Data: In a previous study, we showed that 405-nm light photo-destroys methicillin-resistant Staphy- lococcus aureus (MRSA). The 390‐420 nm spectral width,of the 405-nm superluminous,diode (SLD) source may raise safety concerns in clinical practice, because of the trace of ultraviolet (UV) light within the spectrum. Ob- jective: Here we report the effect of a different wavelength of blue light, one that has no trace of UV, on two strains of MRSA—the US-300 strain of CA-MRSA and the IS-853 strain of HA-MRSA—in vitro. Materials and Methods: We cultured and plated each strain, and then irradiated each plate with 0, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 25, 30, 35, 40, 45, 50, 55, or 60 J/cm,. This same,dose eradicated,91.7% and 94.8% of the aggregate,area of the US-300 and the IS-853 strains, respectively. Conclusion: At practical dose ranges, 470-nm blue light kills HA-MRSA and CA-MRSA in vitro, suggesting that a similar bactericidal effect may be attained in human cases of cuta- neous,and,subcutaneous,MRSA infections. 1