title: Blue 470 nm light suppresses the growth of Salmonella enterica and methicillin-resistant Staphylococcus aureus (MRSA) in vitro.
abstract: OBJECTIVE
  Emerging evidence suggests that blue light can photo-inactivate some bacteria of clinical importance. Consequently, we tested the hypothesis that 470 nm light can suppress growth of two recalcitrant bacteria, MRSA and Salmonella.
  
  
  METHODS
  We plated 5 × 106and 7 × 106CFU/ml USA300 strain of MRSA and 1 × 106CFU/ml of Salmonella enterica serovars Typhimurium and Heidelberg. Plates were irradiated with 55, 110, 165 and 220 J/cm2of blue light, incubated at 37°C for 24 hours and colony counts determined.
  
  
  RESULTS
  Compared with controls, blue light irradiation produced a significant dose-dependent reduction in the number of colonies formed by each bacterial strain (P < 0.001). Irradiation of 5 × 106and 7 × 106CFU/ml MRSA with 55 J/cm2produced 92% (4.6 × 106CFU/ml) and 86% (6 × 106CFU/ml) inactivation respectively, while 110 and 220 J/cm2suppressed each MRSA density 100%. Irradiation of Salmonella Typhimurium with 55 and 110 J/cm2suppressed bacterial growth 31% (3.1 × 105CFU/ml) and 93% (9.3 × 105CFU/ml) respectively; while Salmonella Heidelberg was inhibited 11% (1.1 × 105CFU/ml) and 84% (8.4 × 105CFU/ml) respectively by the two fluences. Complete inactivation of each Salmonella strain was achieved using 165 or 220 J/cm2.
  
  
  CONCLUSIONS
  The observed inhibition of Gram-positive (MRSA) and Gram-negative (Salmonella) bacteria suggests the versatility of blue light in bacteria eradication, making it a viable intervention strategy for decontamination of food and environments that harbor such bacteria. Lasers Surg. Med. 47:595-601, 2015. © 2015 Wiley Periodicals, Inc.
authors.affiliation: College of Health Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, 53211.
authors.forename: Violet V
authors.initials: VV
authors.lastname: Bumah
authors.affiliation: College of Health Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, 53211.
authors.forename: Daniela S
authors.initials: DS
authors.lastname: Masson-Meyers
authors.affiliation: College of Health Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, 53211.|San Diego State University, San Diego, California, 92182.
authors.forename: Chukuka S
authors.initials: CS
authors.lastname: Enwemeka
keywords: Salmonella enterica Heidelberg; Salmonella enterica Typhimurium; bacterial suppression; blue light; methicillin-resistant Staphylococcus aureus; phototherapy