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Optimization of the antimicrobial effect of blue light on methicillin‐resistant Staphylococcus aureus (MRSA) in vitro
Author(s) -
Bumah Violet V.,
MassonMeyers Daniela S.,
Cashin Susan,
Enwemeka Chukuka S.
Publication year - 2015
Publication title -
lasers in surgery and medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 112
eISSN - 1096-9101
pISSN - 0196-8092
DOI - 10.1002/lsm.22327
Subject(s) - staphylococcus aureus , irradiation , bacterial growth , antimicrobial , fluence , microbiology and biotechnology , in vitro , methicillin resistant staphylococcus aureus , optical density , colony forming unit , bacteria , blue light , chemistry , biology , materials science , medicine , optoelectronics , ophthalmology , physics , biochemistry , genetics , nuclear physics
Background and Objective In previous studies, we showed that irradiation with 405 nm or 470 nm light suppresses up to 92% methicillin‐resistant Staphylococcus aureus (MRSA) growth in vitro and that the remaining bacteria re‐colonize. In this study, the aim was to develop a protocol that yields 100% MRSA growth suppression. Materials and Methods We cultured 3 × 10 6 and 5 × 10 6 CFU/ml USA300 strain of MRSA and then irradiated each plate with varying fluences of 1–60 J/cm 2 of 405 nm or 470 nm light, either once or twice at 6 hours intervals. Next, we plated 7 × 10 6 CFU/ml and irradiated it with 45, 50, 55, or 60 J/cm 2 fluence, once, twice, or thrice at the same 6 hours intervals. In a third experiment, the same culture density was irradiated with 0, 165, 180, 220, or 240 J/cm 2 , either once, twice, or thrice. Results Irradiation with either wavelength significantly reduced the bacterial colonies regardless of bacterial density ( P < 0.05). At 3 × 10 6 CFU/ml density, nearly 40% and 50% growth of MRSA were suppressed with as little as 3 J/cm 2 of 405 nm and 470 nm wavelengths, respectively. Moreover, 100% of the colonies were suppressed with a single exposure to 55 or 60 J/cm 2 of 470 nm light or double treatment with 50, 55, or 60 J/cm 2 of 405 nm wavelength. At 5 × 10 6 CFU/ml density, irradiating twice with 50, 55, or 60 J/cm 2 of either wavelength suppressed bacterial growth completely, lower fluences did not. The denser 7 × 10 6 CFU/ml culture required higher doses to achieve 100% suppression, either one shot with 220 J/cm 2 of 470 nm light or two shots of the same dose using 405 nm. Conclusion The bactericidal effect of blue light can be optimized to yield 100% bacterial growth suppression, but with relatively high fluences for dense bacterial cultures, such as 7 × 10 6 CFU/ml. Lasers Surg. Med. 47:266–272, 2015. © 2015 Wiley Periodicals, Inc.