# Evaluation of the Influence of Er:YAG Laser Parameters on the Effectiveness of Growth Inhibition of Candida Biofilms: An In Vitro Study

## TL;DR

This study evaluates how Er:YAG laser settings affect the growth of Candida biofilms in a lab setting.

## Contribution

The paper introduces a systematic in vitro evaluation of Er:YAG laser fluence effects on multiple Candida species biofilms.

## Key findings

- Growth inhibition zones increased with higher laser fluence across all Candida species.
- Viability of mature biofilms decreased significantly with increasing fluence, though some species showed partial recovery at the highest fluence.
- Optimal fluence ranges for biofilm inhibition are species-specific and require further optimization.

## Abstract

Background/Objectives: Candida biofilms exhibit high resistance to antifungal treatment, motivating investigation of adjunctive physical disinfection methods. To quantitatively assess the effect of Er:YAG laser fluence on growth inhibition and viability of single-species Candida biofilms in vitro using a 7 mm full-beam handpiece. Methods: Biofilms of Candida albicans ATCC 10231, C. glabrata ATCC 90030, C. parapsilosis ATCC 22019, and C. krusei ATCC 6258 were grown on Sabouraud agar. In phase 1, growth inhibition zones (GIZs) were evaluated after non-contact Er:YAG irradiation (2 Hz, 300 µs, 10 mm distance, no air or water spray) at fluences from 0.3 to 3.4 J/cm2, with incubation for 24 to 96 h. In phase 2, 96 h mature biofilms were irradiated for 120 s at 0.8, 1.0, 1.5, or 2.0 J/cm2, and viability was quantified by colony-forming unit (CFU) imprinting. All experimental conditions were tested in quadruplicate. Results: GIZ diameters increased significantly with fluence for all species (p < 0.05) and remained stable up to 96 h. At the highest fluence, mean GIZs reached approximately 8.0 mm for C. albicans, 7.7 mm for C. parapsilosis, 7.0 mm for C. krusei, and 5.2 mm for C. glaxfbrata. In mature biofilms, CFU counts decreased significantly with increasing fluence (p < 0.05). For C. albicans, CFUs were reduced from 164.0 ± 25.1 at 0.8 J/cm2 to 16.5 ± 5.2 at 2.0 J/cm2, while C. glabrata decreased from 103.5 ± 5.4 to 20.8 ± 1.7. C. parapsilosis and C. krusei showed maximal reductions at 1.0–1.5 J/cm2, followed by partial CFU rebound at 2.0 J/cm2. Conclusions: Er:YAG irradiation delivered over a large, uniformly illuminated area induces stable, fluence-dependent inhibition and significant reduction of Candida biofilm viability in vitro. Optimal fluence ranges are species specific, underscoring the need for parameter optimization and further evaluation in more complex biofilm models before clinical extrapolation.