Aim: The aim of this paper is to propose a new and reproducible experimental model designed for evaluation of fungicidal effect of type C ultraviolet radiations with a wavelength of 254 nm against medical airborne fungi, and its validation.
Material and method: We achieved a testing module with a continuous monitoring and setting of work parameters (temperature, humidity, exposure time) and a complex device for generating UVC radiations and measurement of dose which offer the possibility to perform experiments in biological and radiological safety conditions. In order to validate this device, we performed some experiments with six strains of airborne fungi (i. e. Aspergillus niger, A. flavus, A. fumigatus, A. ochraceus, A. terreus and Neosartorya fischeri). For testing we used fungal spores suspensions in saline solution with 0.05% Tween 80, having a final concentration of 106 CFU/ml. From each suspension, 0.1 ml have been plated onto Potatoes Dextrose Agar and after drying, the Petri dishes were exposed to UV radiations in a dark field for various periods of time (final doses: 9.3, 27.9, 55.82 and 111.66 mWs/cm^2). After exposure, the plates were rapidly covered with black paper and transferred to incubation in order to prevent DNA photoreactivation. Each test was done in triplicate. After 72-96 hours of incubation, the intensity of fungicidal effect has been calculated using the Ir (decimal logarithmic reduction index).
Results: The Ir values have a linear increment for all tested strains while the UV doses increase. The arithmetic means of Ir were: 3.16 – A. niger, 3.58 – A. flavus, 3.89 – A. fumigatus, 3.96 – A. ochraceus, 4.29 – N. fischeri, 4.41 – A. terreus. The difference of susceptibility for these six species to UVC radiation is not statistical significant (p >> 0.05), but the increase of p values when A. terreus is compared with the remaining strains emphasize some minor differences. Also, no significant differences were observed between the three series of experiments (p>0.05) demonstrating the validation of our model as a reproducible one.
Discussion: We proposed and verified a new experimental model for studying the fungicidal effect of UVC radiations. The tests performed using six strains of spore-forming fungi have proved that our model is a safe, easy to perform and reproducible one. This model may be used for dose evaluation in order to determining the appropriate CFU number reduction for medical airborne fungi in hospitals, pharmaceutical, food and feed industries.