Effect of azoles in Candida glabrata biofilms and its relation with ERG genes expression

Abstract

The occurrence of fungal infections has been significantly increasing, thus contributing to higher morbidity and mortality. The use of broad-spectrum antibiotics, catheters, immunosuppression diseases, chemo and radiotherapy are predisposing factors for invasive fungal infection development. Candida albicans is the predominant species in both health and disease conditions, yet, in the last two decades the number of infections due to non-Candida albicans Candida species has increased significantly. Once believed as non-pathogenic, Candida glabrata rapidly was perceived to be responsible for many human diseases. Despite lacking a number of virulence factors allied to the majority of Candida pathogenicity, C. glabrata possesses high ability to colonize medical devices and human epithelium, resulting generally in biofilms formation ability. Its intrinsically low susceptibility to azoles, such as triazoles (e.g. fluconazole (Flu), voriconazole (Vcz)) and its biofilms tolerance is another problem. The aim of this study was to evaluate the effects of Flu (largely used) and Vcz (hospitalenvironment exclusive) in the control of C. glabrata biofilms and its relation with the expression of genes encoding for Ergosterol: ERG3, ERG6 and ERG11. Three isolates of C. glabrata (vaginal, urine and reference strain) were used. The Minimum Inhibitory Concentration was determined for planktonic cells and biofilms were formed during 24h and treated (for 24h) with different concentrations of both antifungal agents. The effects of Flu and Vcz were analyzed by Colony Forming Units determination and by total biomass quantification using Crystal Violet staining. Biofilms were also analyzed by scanning electron microscopy. Total proteins and carbohydrates were quantified from biofilms’ matrices. Moreover, ergosterol present in the matrices was also quantified by HPLC. To end, qRT-PCR was used to study the gene expression of selected ERG genes. Our results show that, unlike Flu, Vcz had a very good Candida biofilm eradication capacity. No fluctuations between the two azoles were noticed in terms of proteins and carbohydrates, both presenting a blocked production in the first and an overmetabolism in the second. A new finding was the detection of ergosterol in the matrices. The gene expression study showed overexpression of ERG genes, in the presence of the both drug compounds. This work reveals the extraordinary capacity of C. glabrata to change with the purpose of overcome the adversities of the environment. The increase in ergosterol present in matrices and the overexpression of Erg genes could be an explanation for higher C. glabrata biofilms tolerance. This aptitude makes hampered the action of drugs against the cells, and when passing to the progeny, is, undoubtedly, a great advantage to the development of resistance to antifungals, in Candida species.