title: Optimization of the antimicrobial effect of blue light on methicillin-resistant Staphylococcus aureus (MRSA) in vitro.
abstract: 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.
  
  
  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/cm2 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/cm2 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/cm2 of 405 nm and 470 nm wavelengths, respectively. Moreover, 100% of the colonies were suppressed with a single exposure to 55 or 60 J/cm2 of 470 nm light or double treatment with 50, 55, or 60 J/cm2 of 405 nm wavelength. At 5 × 10(6) CFU/ml density, irradiating twice with 50, 55, or 60 J/cm2 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/cm2 of 470 nm light or two shots of the same dose using 405 nm.
  
  
  CONCLUSIONS
  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.
authors: College of Health Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, 53211.
authors: Violet V
authors: VV
authors: Bumah
authors: Daniela S
authors: DS
authors: Masson-Meyers
authors: Susan
authors: S
authors: Cashin
authors: Chukuka S
authors: CS
authors: Enwemeka
mesh_terms: D015169:Colony Count, Microbial; D008027:Light; D055624:Methicillin-Resistant Staphylococcus aureus / Q000528:radiation effects*
keywords: antimicrobial blue light; bacteria suppression; methicillin-resistant Staphylococcus aureus; phototherapy
references: Lasers Surg Med. 2010 Aug;42(6):467-72
references: 20662022
references: Photomed Laser Surg. 2006 Dec;24(6):684-8
references: 17199466
references: Nat Med. 2011 Dec;17(12):1685-91
references: 22057348
references: Cochrane Database Syst Rev. 2010;(9):CD005186
references: 20824842
references: Clin Infect Dis. 2008 Mar 1;46(5):752-60
references: 18220477
references: J Clin Microbiol. 2002 Nov;40(11):4289-94
references: 12409412
references: J Hosp Infect. 1993 Oct;25(2):97-108
references: 7903093
references: Photomed Laser Surg. 2013 Nov;31(11):547-53
references: 23621894
references: BMC Microbiol. 2012;12:176
references: 22894815
references: Lasers Surg Med. 2010 Jan;42(1):38-44
references: 20077489
references: Appl Environ Microbiol. 2009 Apr;75(7):1932-7
references: 19201962
references: Am J Infect Control. 2012 Apr;40(3):194-200
references: 22440670
references: PLoS One. 2013;8(5):e64068
references: 23691149
references: Trends Microbiol. 2008 Aug;16(8):361-9
references: 18585915
references: Photochem Photobiol. 2009 Jan-Feb;85(1):255-60
references: 18764895
references: J Photochem Photobiol B. 1990 May;5(3-4):281-93
references: 2115912
references: Photomed Laser Surg. 2013 Nov;31(11):509-11
references: 24138170
references: J Anesth. 2001;15(1):29-32
references: 14566544
references: Ann Intern Med. 2006 Mar 7;144(5):318-25
references: 16520472
references: Photomed Laser Surg. 2009 Apr;27(2):221-6
references: 19196103
references: BMC Pediatr. 2011;11:96
references: 22032513
references: J Hosp Infect. 2014 Sep;88(1):1-11
references: 25066049
references: Acta Biochim Pol. 2008;55(1):85-90
references: 18217106
references: J Surg Res. 2009 Jul;155(1):111-5
references: 19181335
references: Lasers Surg Med. 2008 Dec;40(10):734-7
references: 19065556
references: Proc Natl Acad Sci U S A. 2009 Apr 7;106(14):5883-8
references: 19293374
references: J Antimicrob Chemother. 2005 Feb;55(2):143-9
references: 15649989
references: Ann Intern Med. 2006 Mar 7;144(5):368-70
references: 16520479
references: J Clin Microbiol. 2006 Jan;44(1):108-18
references: 16390957