Fungicidal Kinetics of Calotropis procera and Bridelia ferruginea Against Multidrug-Resistant Candida Species

Background and aims: Multidrug-resistant (MDR) Candida auris and Candida albicans have emerged as serious hospital-acquired fungal pathogens and are responsible for persistent and hard-to-manage infections worldwide. The increasing prevalence of antifungal resistance, coupled with the limited availability and effectiveness of current therapeutic options, underscores the urgent need to explore alternative antifungal agents. In this context, medicinal plants and their bioactive constituents have gained attention as potential sources of novel antifungal compounds. This study aimed to investigate the antifungal efficacy and time-kill kinetics of leaf extracts from Calotropis procera and Bridelia ferruginea against MDR C. auris and C. albicans. Methods: Leaf materials of both plants were processed and extracted using the maceration technique. Antifungal activity was evaluated through agar well diffusion assays to measure zones of inhibition and by minimum inhibitory concentration determination (MIC). Additionally, time-kill kinetic studies were conducted over a 42 hours at varying extract concentrations to assess the rate and extent of fungicidal activity. Results: Both plant extracts demonstrated inhibitory effects against the tested Candida species (MIC values of 3.125 mg/mL for both). However, C. procera exhibited stronger antifungal activity against C. albicans (16.33 ± 0.33 mm) compared with B. ferruginea (12.67 ± 0.33 mm). Conversely, B. ferruginea showed superior inhibition of C. auris (16.33 ± 0.33 mm) relative to C. procera (12.67 ± 0.33 mm). Time-kill analyses confirmed concentration-dependent and time-dependent fungicidal effects for both extracts. Notably, C. procera rapidly reduced C. albicans viability, achieving a ≥3-log₁₀ reduction within 26–30 hours, whereas B. ferruginea produced a gradual yet sustained decline in C. auris counts throughout the 42-hour assay. Conclusion: The findings revealed species-specific fungicidal properties of the extracts. The rapid action of C. procera against C. albicans and the prolonged activity of B. ferruginea against C. auris suggest complementary antifungal potential, supporting the need for further phytochemical characterization and in vivo evaluation.