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Quantitative Investigation of Efficiency of UV and Visible Light in Eradication of Candida albicans In Vitro

The aim of this study was to quantitatively investigate the efficiency of the ultraviolet (UV) and visible light in eradication of Candida albicans in vitro ; in particular, to determine, for selected wavelengths, the specific eradication coefficients and thresholds in terms of energy density levels required to effect 3.0log10 and 4.0log10 reduction. Oral candidosis is the most common infection of the oral cavity and is caused by Candida species. The widespread use of topical and systemic antifungal agents as conventional treatment for oral candidosis has resulted in the development of resistance in C. albicans. Therefore, it has become necessary to develop alternative therapies for the treatment of oral candidosis. C. albicans ATCC 90028 was irradiated with 254 nm, 365 nm, 406 nm, 420 nm, and broadband Xe spectrum. For each wavelength, a fit of experimental data (survival fraction vs. applied energy density) with an exponential decay function enabled estimation of the specific eradication coefficients and thresholds. Based on estimated specific efficiencies (D) and eradication thresholds (ET) of the investigated wavelengths, the ranking in eradication efficiency of C. albicans (most to least effective) is: 254 nm (D = 6.1mJ/cm - 2, ET99.99 = 56 mJ/cm- 2), broadband Xe spectrum (D= 27.7mJ/cm- 2, ET99.99 = 255mJ/cm- 2), 365 nm (D= 4.3 J/cm- 2, ET99.99 = 39 J/cm- 2), 420 nm (D= 0.65 J/cm- 2, ET99.99 =6 J/cm- 2), and 406nm (D= 11.4 J/cm- 2, ET99.99 = 104 J/cm- 2). The results provide insight into the wavelength-dependent dynamics of eradication of C. albicans. For each investigated wavelength, the eradication coefficient and corresponding eradication threshold were estimated. The observed different eradication efficiencies are consequence of different spectrally dependent inactivation mechanisms. The established methodology enables unambiguous quantitative comparison of eradication efficiencies of optical radiation and selection of most effective wavelengths for clinical and therapeutic use.

Candida albicans; UV; visible spectrum; xenon spectrum;

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