Antifungal Activity and Mechanism of Action of Essential Oil from Piper guineense Against Candida species Isolated from HIV-Positive Patients in Enugu State

Candida species cause life-threatening opportunistic infections in immunocompromised individuals, including HIV-positive patients in whom oral and oesophageal candidiasis represent common AIDS-defining conditions. In South East Nigeria, increasing fluconazole resistance among clinical Candida isolates demands exploration of alternative antifungal agents. Piper guineense, used medicinally across South East Nigeria including Enugu State, produces a piperine and terpenoid-rich essential oil with documented bioactivity. This study evaluates the antifungal activity and mechanism of action of Piper guineense essential oil against fluconazole-susceptible and fluconazole-resistant Candida species isolated from HIV-positive patients at ESUT Teaching Hospital, Enugu. Clinical Candida isolates (C. albicans, C. tropicalis, C. glabrata, C. krusei) were characterised by API 20C AUX and antifungal susceptibility testing by EUCAST broth microdilution. Essential oil composition was determined by GC-MS. MIC and minimum fungicidal concentration (MFC) were determined. Mechanism of action studies included ergosterol binding assays, scanning electron microscopy (SEM), sorbitol and osmoprotection assays, and propidium iodide membrane permeabilisation assays. The essential oil demonstrated MIC values of 0.78 to 6.25 ug/mL against both susceptible and resistant isolates. SEM revealed morphological disruption of cell wall integrity. Membrane permeabilisation and ergosterol binding data confirmed dual membrane-targeting mechanisms. Safrole and terpinen-4-ol were identified as the most likely active constituents. Keywords: Piper guineense, Candida, antifungal, HIV, fluconazole resistance