Antifungal activity of natural extracts from Northeastern Portuguese flowers against Candida biofilms

In healthy individuals, many species of Candida are endogenous commensals of the gastrointestinal and urogenital tracts. However, the prevalence of opportunistic fungal infections (candidosis) has been increasing dramatically over the recent decades and this is particularly evident in immunocompromised individuals. The importance of candidosis is the potential synergistic effect on virulence and subsequent difficulties encountered in treatment. Moreover, a major virulence factor of Candida is its ability to adapt to a variety of different habitats and the consequent formation of surface attached microbial communities known as biofilms. The resistance of Candida biofilms to antifungal agents was first demonstrated by Hawser et al., 1995. Although most episodes of candidosis are attributed to C. albicans, nowadays non-Candida albicans Candida (NCAC), such as C. glabrata, C. tropicalis and C. parapsilosis have emerged as important pathogens and tend to be inherently less susceptible to commonly used antifungal agents. So, in the last years the interest in natural compounds has increased, specifically some phenolic extracts which have been known in folk medicine as antimicrobial agents. Thus, this work aimed to preform a screening of the antifungal potential of phenolic extracts from Castanea sativa, Filipendula ulmaria and Rosa micrantha flowers against Candida biofilms. The extracts were exhaustively characterized by HPLC-DAD-ESI/MS. Hydrolysable tannins were the main group of phenolic compounds in C. sativa and F. ulmaria samples, while flavonoids were the most abundant group in R. micrantha (6090 ± 253 mg/Kg). The minimal inhibitory concentration (MIC) was determined according to the guidelines in NCCLS document M27-A2 with some modifications. All extracts revealed promising antifungal effect, with MIC values ranging from concentrations under 0.05 to 0.625 mg/ml. R. micrantha extract showed a strong effect (MIC ≤ 0.155mg/ml) against all strains tested and, it is also possible to assume that was against C. glabrata and C. parapsilosis that the phenolic extracts showed the highest activity (MIC <0.05mg/ml). Finally, the natural extracts effect was assessed on biofilm formation and on pre-formed biofilms by total biomass quantification using CV staining (1%, v/v). F. ulmaria and R. micrantha were causative agents of important inhibition and destruction of C. tropicalis biofilms. In summary, the significant antifungal activity evident in this work of C. sativa, F. ulmaria and R. micrantha, advise that they could be used as a source of compounds with therapeutic potential against Candida-related infections caused by biofilms.