Jundishapur J Microbiol. 2020 November; 13(11):e111734. Published online 2021 February 27. doi: 10.5812/jjm.111734. Research Article Does Prolonged Exposure of Environmental Fungi to Ultraviolet Irradiation Change the Pattern of Drug Resistance? Ensieh Lotfali 1 , Behshad Valizadeh 2 , Reza Ghasemi 3 and Seyed Amir Hossein Feghhi 2, * 1 Department of Medical Parasitology and Mycology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2 Department of Radiation Application, Shahid Beheshti University, Tehran, Iran 3 Student Research Committee, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran * Corresponding author: Department of Radiation Application, Shahid Beheshti University, Tehran, Iran. Email: a.feghhi@gmail.com Received 2020 December 29; Revised 2021 February 07; Accepted 2021 February 18. Abstract Background: The pathogenic and opportunistic fungal species cause life-threatening infections in immunocompromised patients. The ultraviolet (UV) germicidal irradiation is a well-known method for inactivating a significant number of microorganisms and has wide application for sterilization. Objectives: This study aimed to investigate the effect of ultraviolet C (UV-C) irradiation on the antifungal susceptibility pattern of some filamentous fungi. Methods: The effect of UV-C on the antifungal susceptibility pattern of itraconazole, voriconazole, fluconazole, and amphotericin B against filamentous fungi was examined. Changes in the morphological features of resistant strains following UV-C irradiation were also evaluated using scanning electron microscopy. Results: The results revealed a significant decrease in the number of the surviving spores of strains with the prolongation of UV-C irradiation (0 - 10 to 20 min; P < 0.05). Concerning the morphology of resistant Aspergillus spp., the results of scanning electron microscopy showed a significant increase in the length of irradiated hyphae compared to the non-irradiated hyphae (P < 0.05). In addition, colony count showed a significant decrease (P < 0.05). The findings revealed that UV-C radiation exposure could alter the antifungal susceptibility pattern of Aspergillus spp., such as increasing the minimum inhibitory concentration. Conclusions: Aspergillus spp. can cause systemic infections among lab technicians exposed to different doses of radiation. More- over, this increase in susceptibility pattern can directly affect the duration of treatment. Keywords: Ultraviolet Rays, Aspergillus, Drug Resistance 1. Background Fungi are heterotrophic organisms present in the envi- ronment or in the form of normal flora in humans and an- imals (1, 2). Currently, various fungal species (spp.) cause life-threatening infections in immunocompromised pa- tients, whose population is on a growing trend given the increase in cancer, AIDS, and organ transplantation cases (3). Aspergillosis consists of an extensive range of pul- monary diseases, such as invasive aspergillosis, allergic bronchopulmonary aspergillosis, and type I respiratory hypersensitivity reactions (4). Among Aspergillus spp., As- pergillus flavus is the most common isolate in the environ- ment (5). Alternaria spp. are other airborne fungal agents with different prevalence rates (6). Alternaria alternata is one of the most significant filamentous fungi leading to al- lergic reactions, especially asthma (7). Alternaria spp. can produce a few toxins, including alternariol and alternariol monomethyl ether (8). Verticillium spp. are invasive fun- gal pathogens affecting more than 400 plant species, in- cluding important ornamental, horticultural, agronomi- cal, and woody plants (9). The microbicidal effect of ultraviolet (UV) light is a well-established finding. This light has been used to elimi- nate contaminations in hospitals, the pharmaceutical in- dustry, public buildings, water treatment facilities, fresh food supplies, and agricultural products (10, 11). Ultraviolet ray is divided into the three groups of UVA (320 - 400 nm), UVB (280 - 320 nm), and UVC (200 - 280 nm) based on wave- length (10, 12, 13). Among these types, the UVC ray has the shortest wavelength and the highest energy; as a result, it can induce great effects on spores (14, 15). UV germicidal ir- radiation is a well-known method for inactivating a signifi- cant number of microorganisms and has wide application for sterilization. However, this method is accompanied by Copyright © 2020, Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided the original work is properly cited.