Doron Steinberg,1* Daniel Moreinos,1,2 John Featherstone,3 Moshe
Shemesh,1 and Osnat Feuerstein2
Genetic and Physiological Effects of Noncoherent Visible Light
Combined with Hydrogen Peroxide on Streptococcus mutans in Biofilm
Antimicrobial Agents and Chemotherapy, July 2008, p. 2626-2631, Vol.
52, No. 7

Institute of Dental Sciences, Faculty of Dental Medicine, Hebrew
University—Hadassah, Jerusalem, Israel,1 Department of Prosthodontics,
Faculty of Dental Medicine, Hebrew University—Hadassah, Jerusalem,
Israel,2 School of Dentistry, University of California San Francisco,
San Francisco, California3

Received 25 December 2007/ Returned for modification 4 February 2008/
Accepted 25 February 2008

Oral biofilms are associated with the most common infections of the
oral cavity. Bacteria embedded in the biofilms are less sensitive to
antibacterial agents than planktonic bacteria are. Recently, an
antibacterial synergic effect of noncoherent blue light and hydrogen
peroxide (H2O2) on planktonic Streptococcus mutans was demonstrated.
In this study, we tested the effect of a combination of light and H2O2
on the vitality and gene expression of S. mutans embedded in biofilm.
Biofilms of S. mutans were exposed to visible light (wavelengths, 400
to 500 nm) for 30 or 60 s (equivalent to 34 or 68 J/cm2) in the
presence of 3 to 300 mM H2O2. The antibacterial effect was assessed by
microbial counts of each treated sample compared with that of the
control. The effect of light combined with H2O2 on the different
layers of the biofilm was evaluated by confocal laser scanning
microscopy. Gene expression was determined by real-time reverse
transcription-PCR. Our results show that noncoherent light, in
combination with H2O2, has a synergistic antibacterial effect through
all of the layers of the biofilm. Furthermore, this treatment was more
effective against bacteria in biofilm than against planktonic
bacteria. The combined light and H2O2 treatment up-regulated the
expression of several genes such as gtfB, brp, smu630, and comDE but
did not affect relA and ftf. The ability of noncoherent visible light
in combination with H2O2 to affect bacteria in deep layers of the
biofilm suggests that this treatment may be applied in biofilm-related
diseases as a minimally invasive antibacterial procedure.

* Corresponding author. Mailing address: Institute of Dental Sciences,
Faculty of Dental Medicine, Hebrew University—Hadassah, P.O. Box
12272, Jerusalem 91120, Israel. Phone: 972-2-6757633. Fax:
972-2-6758561. E-mail: dorons@cc.huji.ac.il

Published ahead of print on 3 March 2008.

Antimicrobial Agents and Chemotherapy, July 2008, p. 2626-2631, Vol.
52, No. 7
Copyright © 2008, American Society for Microbiology.
http://aac.asm.org/cgi/content/abstract/52/7/2626