Enhanced germicidal effects of pulsed UV-LED irradiation on biofilms

Abstract

Aims: 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. Methods and 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. Significance and Impact of the Study: This study can assist in developing a low‐frequency pulsed UVA‐LED system to be applied to pathogenic biofilms for disinfection.

Biofilm formation of Candida albicans on implant overdenture materials and its removal

“…Candida biofilms were developed using a modified method described by Jin et al 17 Briefly, C. albicans CAD1, a clinical isolate, suspension was diluted to a final concentration of 10 6 colony-forming units (CFU)/mL with yeast nitrogen base/100 mM glucose medium supplemented with 2.5 mM N-acetylglucosamine. 15,18 Saliva-coated or uncoated samples were incubated in 1 mL of Candida suspension aerobically for 90 min (adhesion phase) at 37 8C, and then gently rinsed twice with PBS to remove non-adherent cells. Subsequently, samples were aerobically incubated in the medium for 2 days at 37 8C (biofilm formation phase).…”

Quantitative Investigation of Efficiency of Ultraviolet and Visible Light in Eradication ofCandida albicans In Vitro

“…9 Although PDT is more usually applied for treating cancer, it has been demonstrated that PDT is effective against oral species and may not promote damage to host cells and tissues. 10 Another promising approach, which is potentially less complicated and less harmful than PDT, is use of ultraviolet (UV) [11][12][13][14][15][16][17] or visible (VIS) incoherent light. [18][19][20] Although the application of the UV or VIS light in therapy seems promising, and deserves an intensive investigation, far less effort has been put into research following this approach in comparison with PDT.…”

Effects of UV-A LED light irradiation on growth of cultured RAW 264.7 cells

“…The antioxidant capacity value of mannitol to ROS is low (Choi et al 2007), and although mannitol abolished PDT-stimulated intracellular oxidative stress, PDT-induced apoptotic changes in cells were not affected (Chan and Wu 2004). One reason might be that mannitol is membrane-impermeable, and its scavenging ability against singlet oxygen is low because it is a scavenger of hydroxyl radicals (Li et al 2010). The addition of NAC not only restored cell growth that was inhibited by UV-A, but also stimulated cell proliferation of non-irradiated cells (Figure 4).…”