title: Enhanced germicidal effects of pulsed UV-LED irradiation on biofilms.
abstract: OBJECTIVE
  The major objective of the study was to evaluate the enhanced germicidal effects of low-frequency pulsed ultraviolet A (UVA)-light-emitting diode (LED) on biofilms.
  
  
  RESULTS
  The germicidal effects of UVA-LED irradiation (365 nm, 0·28 mW cm(-2) , in pulsed or continuous mode) on Candida albicans or Escherichia coli biofilms were evaluated by determining colony-forming units. The morphological change of microbial cells in biofilms was observed using scanning electron microscopy. After 5-min irradiation, over 90% of viable micro-organisms in biofilms had been killed, and pulsed irradiation (1-1000 Hz) had significantly greater germicidal ability than continuous irradiation. Pulsed irradiation (100 Hz, 60 min) almost completely killed micro-organisms in biofilm (>99·9%), and 20-min irradiation greatly damaged both microbial species. Interestingly, few hyphae were found in irradiated Candida biofilms. Moreover, mannitol treatment, a scavenger of hydroxyl radicals (OH(•) ), significantly protected viable micro-organisms in biofilms from UVA-LED irradiation.
  
  
  CONCLUSIONS
  The study demonstrated that pulsed UVA-LED irradiation has a strong germicidal effect (maximum at 100 Hz, over 5-min irradiation) and causes the disappearance of hyphal forms of Candida.
  
  
  CONCLUSIONS
  This study can assist in developing a low-frequency pulsed UVA-LED system to be applied to pathogenic biofilms for disinfection.
authors.affiliation: Department of Oral and Maxillofacial Prosthodontics and Oral Implantology, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Li
authors.forename: K
authors.initials: K
authors.lastname: Hirota
authors.forename: H
authors.initials: H
authors.lastname: Yumoto
authors.forename: T
authors.initials: T
authors.lastname: Matsuo
authors.forename: Y
authors.initials: Y
authors.lastname: Miyake
authors.forename: T
authors.initials: T
authors.lastname: Ichikawa
mesh_terms: D018441:Biofilms / Q000528:radiation effects*; D002176:Candida albicans / Q000528:radiation effects*; D015169:Colony Count, Microbial; D004203:Disinfection / Q000379:methods*; D004926:Escherichia coli / Q000528:radiation effects*; D016166:Free Radical Scavengers / Q000494:pharmacology; D017665:Hydroxyl Radical / Q000378:metabolism; D008353:Mannitol / Q000494:pharmacology; D050296:Microbial Viability; D014466:Ultraviolet Rays
chemical_list: D016166:Free Radical Scavengers; D017665:Hydroxyl Radical; D008353:Mannitol