Antifungal effects of Nigella sativa L. (Black cumin) seed extracts and seed oil on selected Candida albicans strains

Abstract

The seed extracts of Nigella sativa (black cumin) have been used in different civilizations around the world for centuries to treat various animal and human ailments. C. albicans is a member of the normal human microbiome, but under certain circumstances it can cause infections that range from superficial infections of the skin to life-threatening systemic infections. Resistance to antifungal drugs in C. albicans has been on the increase in recent years. Several factors such as biofilm formation and overexpression of genes for efflux drug pump have been identified to contribute to the pathogenic potential of this fungus. This research examined antifungal effects of black cumin seed extracts and seed oil on C albicans wild-type (C1 and C2) and URA3 delete (CAF2 and CAI4) strains. Effects of the extracts on the key genes (MDS3 and MDR1) involved in drug resistance in C. albicans were also investigated. Aqueous and methanol extracts of the plant seeds were prepared using standard procedure. Aqueous and methanol extracts of N. sativa seeds, as well as the seed oil, were used for antimicrobial screening and for the analysis of effects on drug resistance genes using agar well diffusion technique, while fluconazole was used as a standard drug. The seed oil, as well as the aqueous and methanolic seed extracts of N. sativa greatly inhibited the wild-type clinical isolates C1 and C2. Interestingly, the URA3-delete strains were only inhibited by the oil. The amplification of the target genes in the various strains presented some intriguing results, with the gene(s) detected only prior to exposure or after exposure to the agent or at both instances. N. sativa, particularly the seed oil, has proven to have antifungal effects on fluconazole-resistant C. albicans with varying effects on the resistant genes.