Mechanism of Visible Light Phototoxicity on Porphyromonas gingivalis and Fusobacterium nucleatum

Abstract

Phototoxicity of visible light laser on the porphyrin-producing bacteria, Porphyromonas gingivalis, in the absence of photosensitizers and under aerobic conditions was shown in previous studies. Recently, we found that the noncoherent visible light sources at wavelengths of 400-500 nm, commonly used in restorative dentistry, induced a phototoxic effect on P. gingivalis, as well as on Fusobacterium nucleatum, and to a lesser extent on the Streptococci sp. To elucidate the mechanism of this phototoxic effect, P. gingivalis and F. nucleatum were exposed to light (1) under aerobic and anaerobic environments and (2) in the presence of scavengers of reactive oxygen species (ROS). Phototoxic effect was not observed when the bacteria were exposed to light under anaerobic conditions. Dimethyl thiourea, a hydroxyl radical scavenger, was effective in reducing phototoxicity (P </= 0.05). Other scavengers, such as catalase, superoxide dismutase and ascorbic acid, were less effective when applied separately. These results support the assumption that the phototoxic effect of blue light on the periopathogenic bacteria is oxygen dependent and that hydroxyl radicals play an important role in this process.

The Quorum Sensing-Dependent Gene katG of Burkholderia glumae Is Important for Protection from Visible Light

“…Under oxidative-stress conditions, KatG of B. pseudomallei plays important roles in cell survival (22). The phototoxic effect of visible light on bacteria is oxygen dependent (7). For example, exposing Porphyromonas gingivalis and Fusobacterium nucleatum to blue light under anaerobic conditions eliminates the phototoxic effect seen under aerobic conditions (7).…”

“…The phototoxic effect of visible light on bacteria is oxygen dependent (7). For example, exposing Porphyromonas gingivalis and Fusobacterium nucleatum to blue light under anaerobic conditions eliminates the phototoxic effect seen under aerobic conditions (7). The katG mutation in B. glumae did not affect survival at the stationary growth phase but was lethal when the strain was exposed to visible light.…”

Inactivation of Bacterial Pathogens following Exposure to Light from a 405-Nanometer Light-Emitting Diode Array

“…Previous studies have shown that exposure to visible light, more specifically, blue-light wavelengths, causes inactivation of certain bacterial species, including Propionobacterium acnes, Helicobacter pylori, and some oral pigmented bacteria (1,8,22). This inactivation mechanism, known to be oxygen dependent (6), is thought to be a result of the photoexcitation of naturally occurring endogenous porphyrins, which act as endogenous photosensitizers within the bacterial cells. This porphyrin excitation leads to energy transfer and, ultimately, the production of highly cytotoxic, oxygenderived species, most notably, singlet oxygen (11,26).…”

Genetic and Physiological Effects of Noncoherent Visible Light Combined with Hydrogen Peroxide on Streptococcus mutans in Biofilm

“…However, a dose-dependent synergistic antibacterial effect on bacteria embedded in biofilm was demonstrated when noncoherent blue light and H 2 O 2 were applied simultaneously. It was previously shown that the phototoxic effect of noncoherent blue light on planktonic bacteria involves the formation of ROS and that hydroxyl radicals (OH ⅐ ) play an important role in this process (4,5). It is assumed that the synergistic effect on bacterial vitality in biofilm is the result not of direct fission of H 2 O 2 by light, as described for the mechanism of action of UV light, but of the generation of the highly reactive OH ⅐ radical when H 2 O 2 encounters "free Fe(II)," via the Fenton reaction (5).…”

“…Recently, a synergistic antibacterial effect of noncoherent blue light, often used in restorative dentistry, and hydrogen peroxide (H 2 O 2 ) on S. mutans under planktonic conditions was observed (5). Due to the widespread use of antibiotics and the emergence of more resistant and virulent strains of microorganisms, there is an urgent need to develop alternative sterilization technologies that affect biofilms.…”