Growth inhibition of Trichophyton rubrum by laser irradiation: exploring further experimental aspects in an in vitro evaluation study

Abstract

Background According to the results of the clinical trials, laser therapy is effective for the treatment of onychomycosis, but the in vitro findings are inconsistent among studies. This study aimed to explore the experimental conditions of laser for the inhibition of Trichophyton rubrum growth in vitro. A 1064-nm neodymium-doped yttrium aluminum garnet (Nd:YAG) laser was used to irradiate colonies using a small (6-mm diameter) or large (13-mm diameter) area, and using 300, 408, or 600 J/cm2. The surface temperature of the colony was measured after irradiation and every 2 min. The growth area was calculated until the 7th or 10th day of incubation daily. Results For the small area group, at 300 J/cm2, the immediate surface temperature was 25.2 ± 0.2°C, but without effect on growth (P = 0.516). At 408 J/cm2, the immediate surface temperature was 32.0 ± 0.4°C; growth was inhibited for 7 days (P < 0.001). At 600 J/cm2, the immediate surface temperature was 38.1 ± 0.4°C; the growth was completely stopped for at least 10 days (P < 0.001). For the large area group, the temperature patterns were similar to those of the small area group, but the highest temperature was lower than in the small area groups, and no growth inhibition effect was observed (all P > 0.05). Conclusions When the irradiation area is small, a 1064-nm Nd:YAG laser at 408 or 600 J/cm2 can be effective in suppressing T. rubrum growth in vitro.

Nd:YAG 1064 nm laser treatment for onychomycosis ‐ is it really effective? A prospective assessment for efficiency and factors contributing to response

“…Both in vitro and clinical studies have demonstrated significant growth inhibition of T. rubrum and other species by Nd:YAG laser treatment 24,37,38 . The microbiocidal impact of the deeply penetrating Nd:YAG 1064 nm laser has been linked to the resulting hyperthermia and its denaturing effect on critical cellular proteins and structures 39,40 .…”

“…Both in vitro and clinical studies have demonstrated significant growth inhibition of T. rubrum and other species by Nd:YAG laser treatment. 24,37,38 The microbiocidal impact of the deeply penetrating Nd:YAG 1064 nm laser has been linked to the resulting hyperthermia and its denaturing effect on critical cellular proteins and structures. 39,40 The localised rise in temperature has also been hypothesized to activate stress responses, including increased uptake and presentation of foreign particles and microbe, generation of reactive oxygen species and apoptosis.…”