Comparative Antifungal Screening of Three Nigella sativa Seed Extract Preparations Against Medically Relevant Fungi

Abstract

Extracts from plant sources have been found to display significant variability in terms of their spectrum of antifungal activities because of the influence of extraction processes on the types of secondary metabolites obtained. In this case, three coded extracts of Nigella sativa seeds (ES, ESM, and CS) were tested at a screening concentration on various fungi (Candida spp., Cryptococcus spp., Aspergillus spp., Penicillium spp., and Coccidioides spp.) using agar diffusion. ES preparation displayed inhibition against Candida spp. (27 mm) and Cryptococcus spp. (41 mm), whereas the ESM preparation inhibited Candida spp. (39 mm), Penicillium spp. (50 mm), and Coccidioides spp. (49 mm). On the other hand, CS preparation inhibited Aspergillus spp. (24 mm), Coccidioides spp. (40 mm), and Cryptococcus spp. (42 mm). Solvent control did not display any inhibition. The response table showed that there is selectivity of preparation on fungi rather than broad spectrum activity by each preparation. Descriptive average inhibition zones are 13.6 mm for ES, 27.6 mm for ESM, and 21.2 mm for CS. These averages indicate the taxonomic coverage and not replicated treatment effect. These results highlight extract-fungus pairs for confirmation and further characterization by broth microdilution tests and compound identification. Since the data was non-replicated and compounds' identity was not available, inferential statistical tests, MIC, and molecular docking were not carried out. The study recommends coded extracts screening as an initial step in the process but highlights the necessity of isolate authentication, independent extraction batches, antifungal control, MIC/MFC test, and identification of active compounds.