Background and Aim: Candida albicans, the most common human fungal commensal pathogen, is a normal member of the human microbiota which can colonize the oral cavity, vagina and gastrointestinal tract. This opportunistic pathogen can cause diseases ranging from mucosal infections to systemic mycoses, depending on the vulnerability and weakness of the immune system of the host. In addition, it is the most common cause of septicemia with 50-100% mortality. Ultraviolet-B (UV-B) radiation is an electromagnetic radiation with a wavelength of 100-400 nm. It reduces the synthesis of proteins and nucleic acids, retards growth, and causes mutation in eukaryotic and prokaryotic cells. Previous investigators have reported on the different effects of UV irradiation on Candida albicans including cidal effect, inhibitory growth, as well as phenotype switching. In the present study we investigated the effect of UV-B irradiation on C. albicans’s growth in a solid medium, production of chlamydoconidia, carbohydrate assimilation and pathogenesis in mice.

  Material and Methods: C. albicans was grown in a SC medium, followed by incubation at 30° C for 24 hours and irradiating the cells with UV-B for 5,10,15,20 min at 302 nm wavelength by transilluminator. A sample of non-irradiated yeast cells served as control.

  Results: After 24, 48 and 72 hours of irradiation growth rate was reduced, the maximum reduction occurring after 20 minute. There was no difference between irradiated and non-irradiated C. albicans samples as regards sugars assimilation. Irradiation could inhibit production of chlamidoconidia by the fungus, the magnitude of inhibition increasing with increasing length of exposure to irradiation, such that after 20 minutes no chlamidoconidia could be seen in the medium. Further analysis of the data showed that pathogenicities of the fungus in irradiated and control samples were not statistically different. Neither was there any difference between them as regards size or number of bands of DNA molecules on 1% agarose gel.

  Conclusion: The findings throw some light on how UVB irradiation can affect the phenotype of C. albicans isolates. Certainly more studies, e.g., on gene regulation, are required to find the effects of UVB at the molecular level in this fungus.