title: Violet 405 nm light: A novel therapeutic agent against β-lactam-resistant Escherichia coli.
abstract: OBJECTIVE
  Approximately 1.7 million patients are affected by hospital-acquired infections every year in the United States. The increasing prevalence of multidrug-resistant bacteria associated with these infections prompts the investigation of alternative sterilization and antibacterial therapies. One method currently under investigation is the antibacterial properties of visible light. This study examines the effect of a visible light therapy (VLT) on β-lactam-resistant Escherichia coli, a common non-skin flora pathogen responsible for a large percentage of indwelling medical device-associated clinical infection.
  
  
  METHODS
  405 nm light-emitting diodes were used to treat varying concentrations of a common laboratory E. coli K-12 strain transformed with the pCIG mammalian expression vector. This conferred ampicillin resistance via expression of the β-lactamase gene. Bacteria were grown on sterile polystyrene Petri dishes plated with Luria-Bertani broth. Images of bacterial growth colonies on plates were processed and analyzed using ImageJ. Irradiance levels between 2.89 ± 0.19 and 9.45 ± 0.63 mW cm(-2) and radiant exposure levels between 5.60 ± 0.39 and 136.91 ± 4.06 J cm(-2) were tested.
  
  
  RESULTS
  VLT with variable irradiance and constant treatment time (120 minutes) demonstrated significant reduction (P < 0.001) in E. coli between an irradiance of 2.89 mW cm(-2) (81.70%) and 9.37 mW cm(-2) (100.00%). Similar results were found with variable treatment time with constant irradiance. Log10 reduction analysis produced between 1.98 ± 0.53 (60 minute treatment) and 6.27 ± 0.54 (250 minute treatment) log10 reduction in bacterial concentration (P < 0.001).
  
  
  CONCLUSIONS
  We have successfully demonstrated a significant bacterial reduction using high intensity 405 nm light. Illustrating the efficacy of this technology against a β-lactam-resistant E. coli is especially relevant to the need for novel methods of sterilization in healthcare settings. These results suggest that VLT using 405 nm light could be a suitable clinical option for eradication of β-lactam-resistant E. coli. Visible light kills statistically significant concentrations of E. coli. Antibiotic-resistant Gram-negative bacteria exhibits sensitivity to 405 nm light. Greater than 6 log10 reduction in β-lactam-resistant E. coli when treated with visible light therapy.
authors.affiliation: Department of Bioengineering, University of Utah, Salt Lake City, Utah, 84112.
authors.forename: Nathaniel L R
authors.initials: NL
authors.lastname: Rhodes
authors.affiliation: Department of General Surgery, University of Utah, Salt Lake City, Utah, 84132.
authors.forename: Martin
authors.initials: M
authors.lastname: de la Presa
authors.affiliation: School of Medicine, Oregon Health and Sciences University, Portland, Oregon, 97239.
authors.forename: Mitchell D
authors.initials: MD
authors.lastname: Barneck
authors.affiliation: Department of Bioengineering, University of Utah, Salt Lake City, Utah, 84112.
authors.forename: Ahrash
authors.initials: A
authors.lastname: Poursaid
authors.affiliation: Department of General Surgery, University of Utah, Salt Lake City, Utah, 84132.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Firpo
authors.affiliation: Department of Bioengineering, University of Utah, Salt Lake City, Utah, 84112.|Department of General Surgery, University of Utah, Salt Lake City, Utah, 84132.
authors.forename: John T
authors.initials: JT
authors.lastname: Langell
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D004203:Disinfection / Q000379:methods*; D024881:Drug Resistance, Bacterial / Q000528:radiation effects*; D048168:Escherichia coli K12 / Q000187:drug effects / Q000254:growth & development / Q000528:radiation effects*; D008027:Light; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams
keywords: antibiotic resistance; sterilization; ultraviolet (UV) light; visible light therapy; visible spectrum light