title: Antimicrobial activity of hydroxyl radicals generated by hydrogen peroxide photolysis against Streptococcus mutans biofilm.
abstract: Prevention of dental caries with maximum conservation of intact tooth substance remains a challenge in dentistry. The present study aimed to evaluate the antimicrobial effect of H2O2 photolysis on Streptococcus mutans biofilm, which may be a novel antimicrobial chemotherapy for treating caries. S. mutans biofilm was grown on disk-shaped hydroxyapatite specimens. After 1-24 h of incubation, growth was assessed by confocal laser scanning microscopy and viable bacterial counting. Resistance to antibiotics (amoxicillin and erythromycin) was evaluated by comparing bactericidal effects on the biofilm with those on planktonic bacteria. To evaluate the effect of the antimicrobial technique, the biofilm was immersed in 3% H2O2 and was irradiated with an LED at 365 nm for 1 min. Viable bacterial counts in the biofilm were determined by colony counting. The thickness and surface coverage of S. mutans biofilm increased with time, whereas viable bacterial counts plateaued after 6 h. When 12- and 24-h-old biofilms were treated with the minimum concentration of antibiotics that killed viable planktonic bacteria with 3 log reduction, their viable counts were not significantly decreased, suggesting the biofilm acquired antibiotic resistance by increasing its thickness. By contrast, hydroxyl radicals generated by photolysis of 3% H2O2 effectively killed S. mutans in 24-h-old biofilm, with greater than 5 log reduction. The technique based on H2O2 photolysis is a potentially powerful adjunctive antimicrobial chemotherapy for caries treatment.
authors.affiliation: Laboratory for Redox Regulation, Tohoku University Graduate School of Dentistry, 4-1 Seiryo, Aoba-ku, Sendai 980-8575, Japan. Electronic address: keisuke@m.tohoku.ac.jp.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Nakamura
authors.affiliation: Laboratory for Redox Regulation, Tohoku University Graduate School of Dentistry, 4-1 Seiryo, Aoba-ku, Sendai 980-8575, Japan.
authors.forename: Midori
authors.initials: M
authors.lastname: Shirato
authors.affiliation: Division of Molecular and Regenerative Prosthodontics, Tohoku University Graduate School of Dentistry, 4-1 Seiryo, Aoba-ku, Sendai 980-8575, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Kanno
authors.affiliation: Department of Clinical Dentistry, Faculty of Health Sciences, The Arctic University of Norway, Tromsø 9037, Norway; Department of Cariology, Institute of Odontology, Sahlgrenska Academy, University of Gothenburg, SE-405 30 Gothenburg, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Örtengren
authors.affiliation: Department of Cariology, Institute of Odontology, Sahlgrenska Academy, University of Gothenburg, SE-405 30 Gothenburg, Sweden.
authors.forename: Peter
authors.initials: P
authors.lastname: Lingström
authors.affiliation: Laboratory for Redox Regulation, Tohoku University Graduate School of Dentistry, 4-1 Seiryo, Aoba-ku, Sendai 980-8575, Japan.
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Niwano
mesh_terms: D000891:Anti-Infective Agents, Local / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects*; D015169:Colony Count, Microbial; D006861:Hydrogen Peroxide / Q000378:metabolism*; D017665:Hydroxyl Radical / Q000494:pharmacology*; D050296:Microbial Viability / Q000187:drug effects; D018613:Microscopy, Confocal; D010782:Photolysis; D013295:Streptococcus mutans / Q000187:drug effects* / Q000502:physiology
chemical_list: D000891:Anti-Infective Agents, Local; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide
keywords: Biofilm; Confocal laser scanning microscopy; Hydrogen peroxide; Hydroxyl radical; Photolysis; Streptococcus mutans