Abstract
The aim of our work was to check if one of the products of natural origin, namely honey bee propolis, may be an alternative or supplement to currently used antifungal agents. The activity of 50 ethanolic extracts of propolis (EEPs), harvested in Polish apiaries, was tested on a group of 69 clinical isolates of C. albicans. Most of the EEPs showed satisfactory activity, with minimum fungicidal concentrations (MFC) mainly in the range of 0.08–1.25% (v/v). Eradication of biofilm from polystyrene microtitration plates in 50% (MBEC50, Minimum Biofilm Eradication Concentration) required concentrations in the range of 0.04% (v/v) to more than 1.25% (v/v). High activity was also observed in eradication of biofilm formed by C. glabrata and C. krusei on the surfaces of PVC (Polyvinyl Chloride) and silicone catheters. EEPs at subinhibitory concentrations inhibited yeast-to-mycelia morphological transformation of C. albicans in liquid medium and mycelial growth on solid medium. A synergistic effect was observed for the action of EEP in combination with fluconazole (FLU) and voriconazole (VOR) against C. albicans. In the presence of EEP at concentrations as low as 0.02%, the MICs of FLU and VOR were 256 to 32 times lower in comparison to those of the drug alone. Evidence for the fungal cell membrane as the most probable target of EEPs are presented.
Highlights
An increasing number of fungal infections is an alarming problem, especially for immunocompromised patients
Ethanolic extracts prepared from 50 propolis samples (EEPs) collected from different regions of northern Poland were tested for their anti Candidal in vitro activity against planktonic C. albicans and C. glabrata cells
The minimum fungicidal concentrations (MFC) value equal to 0.63% was established for 15 ethanolic extracts of propolis (EEPs) and 0.31% for eight EEPs
Summary
An increasing number of fungal infections is an alarming problem, especially for immunocompromised patients. Candida albicans species have been recorded as the most frequent cause of life threatening disseminated candidiasis, representing up to 60% of isolates. Non-albicans Candida spp. resistant to conventional treatments has emerged as prevalent causes of candidiasis, including C. parapsilosis, C. tropicalis and C. glabrata [1,2]. C. albicans, other Candida spp. as well as other pathogenic yeasts have developed different mechanisms of resistance against antifungal agents, including mutations of genes coding for molecular targets of azoles, echinocandins or flucytosine and overexpression of drug transporters [3,4,5]. Many nosocomial-acquired infections are associated with the use of medical devices (e.g., catheters), which are the sites for fungal biofilm development. Cells living in biofilm produce an extracellular matrix (ECM) composed of Pathogens 2018, 7, 56; doi:10.3390/pathogens7020056 www.mdpi.com/journal/pathogens
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