In vitro anti-Candida activity of Glycyrrhiza glabra L.

Abstract

2 AbstractThe severity and frequency of opportunistic fungal infections still growing, concomitantly to the increasing rates of antimicrobial drug's resistance. Natural matrices have been used over years due to its multitude of health benefits, including antifungal potential. Thus, the present work aims to evaluate the anti-Candida potential of the phenolic extract and individual phenolic compounds of Glycyrrhiza glabra L.(licorice), by disc diffusion assay, followed by determination of the minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) for both planktonic cells and biofilms.Licorice extract evidenced inhibitory potential against the nineteen tested Candida strains, but no pronounced effect was observed by testing the most abundant individual phenolic compounds. Candida tropicalis strains were the most sensible, followed by Candida glabrata, Candida parapsilosis and, then, Candida albicans. Lower MIC and MFC values were achieved to C. glabrata and C. tropicalis, which confirms its susceptibility to licorice extract; however, for C. tropicalis strains a higher variability was observed. Anti-biofilm potential was also achieved, being most evident in some C. glabrata and C. tropicalis strains. In general, a twice concentration of the MIC was necessary for planktonic cells to obtain a similar potential to that one observed for biofilms. Thus, an upcoming approach for new antifungal agents, more effective and safer than the current ones, is stablished; notwithstanding, further studies are necessary in order to understand its mechanism of action, as also to assess kinetic parameters.

Susceptibility testing of Candida albicans and Candida glabrata to Glycyrrhiza glabra L.

“…Therefore, it is very important to search and to develop efficient antifungal agents. Considering the highly effective in vitro anti-Candida activity evidenced by licorice methanol: water extract in previous experiments (Martins et al, 2016) and that the mechanism of action of this plant extract is poorly understood, it becomes essential to deepen knowledge on biocidal effect of licorice. In this sense, reference strains from C. albicans and C. glabrata species were selected to determine the effect of licorice extract on its cells by flow cytometry and transmission electron microscopy.…”

“…The concentration tested in this study (1.5 mg/mL) was based on the obtained results for minimal inhibitory (MIC) and minimal fungicidal (MFC) concentrations (Martins et al, 2016), and prepared from a licorice stock solution of 50 mg/mL. Sterile water was used as solvent.…”

“…The licorice extract concentration (1.5 mg/mL) was selected taking into consideration the previous results obtained (Martins et al, 2016) on the assessment of the anti-Candida activity in planktonic and their respective biofilms cells: C. albicans ATCC 90028 (MIC/MFC ≥ 1.5 mg/mL), C. glabrata ATCC 2001 (MIC = 0.75 mg/mL; MFC = 1.5 mg/mL). Both strains were from the archive collection of the biofilm group of the Centre of Biological Engineering, University of Minho, Braga − Portugal.…”

“…To perform the assessment of the effective mode of action of licorice extract on Candida species, a standard concentration of 1.5 mg/mL was used, based on the results obtained in the previous study (Martins et al, 2016).…”

“…Considering the previous results obtained to licorice extract (completely characterized in terms of phenolic composition), namely antioxidant (Martins et al, 2015a) and anti-Candida (Martins et al, 2016) activities, the present study aims to access the effect of licorice extract on cell integrity and cultivability of the most problematic and virulent Candida species, namely Candida albicans and Candida glabrata species (Martins et al, 2015c). The main aspects that triggered the development of this experiment was to understand in which manner licorice exerted its anti-Candida potential, once no visible effects were observed when isolated phenolic compounds present in the extract were tested separately, while with the whole extract a prominent effect was reached.…”