title: Photochemical eradication of methicillin-resistant Staphylococcus aureus by blue light activation of riboflavin.
abstract: OBJECTIVE
  To compare elimination of methicillin-resistant Staphylococcus aureus (MRSA) by exposure of blue light alone and with riboflavin.
  
  
  METHODS
  A reference strain of MRSA was cultured and diluted in PBS with and without riboflavin (0.01%). Fifteen microlitre was added on a microscope slide, creating a fluid layer with a thickness of around 400 microns. Both of the bacterial suspensions were exposed to blue light, and the effect between exposure with and without riboflavin was compared. Evaluation involved two different wavelengths (412 and 450 nm) of blue light with a lower (5.4 J/cm2) and higher dose (approximately 28.5 J/cm2). The effect of 412 nm light was also evaluated for a thicker fluid layer (1.17 mm). After exposure, colony-forming units (CFUs) were determined for each solution. All measurements were repeated eight times.
  
  
  RESULTS
  The reductions in bacteria were similar for both wavelengths. With riboflavin, a statistically significant elimination was observed for both 412 and 450 nm (p < 0.001). At both dosages, the mean reduction was more pronounced with the presence of riboflavin than without it. Using the higher dose, CFU reduction was 99% and 98%, respectively, for 412 and 450 nm light. The bactericidal efficacy was high also in the deeper fluid layer (93%, higher dose).
  
  
  CONCLUSIONS
  Riboflavin enhanced the antibacterial effect on the exposed MRSA strain of blue light for both 412 and 450 nm blue light. This indicates that blue light could be considered for possible implementation in deep corneal infections.
authors.affiliation: Department of Ophthalmology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
authors.forename: Karim
authors.initials: K
authors.lastname: Makdoumi
authors.affiliation: Terumo BCT, Inc., Lakewood, CO, USA.
authors.forename: Ray
authors.initials: R
authors.lastname: Goodrich
authors.affiliation: Clinical Research Centre, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Bäckman
mesh_terms: D015169:Colony Count, Microbial; D003315:Cornea / Q000187:drug effects / Q000382:microbiology; D015818:Eye Infections, Bacterial / Q000188:drug therapy* / Q000382:microbiology; D006801:Humans; D007634:Keratitis / Q000188:drug therapy* / Q000382:microbiology; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology; D012256:Riboflavin / Q000494:pharmacology*; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D014466:Ultraviolet Rays
chemical_list: D017319:Photosensitizing Agents; D012256:Riboflavin
keywords: PACK-CXL; blue light; collagen cross-linking; keratitis; riboflavin