Essential oil of Zingiber spectabile griff.: a potential antiamoebic agent against Acanthamoeba castellanii

Pathogenic Acanthamoeba castellanii can cause blinding keratitis and fatal granulomatous amoebic encephalitis. Current treatments for Acanthamoeba infections have shown limited efficacy, posing a challenge in the effective management of amoebic infections. Medicinal plants and their bioactive compounds have shown promise against microbial infections. Herein, essential oil obtained by hydrodistillation of the rhizomes of Zingiber spectabile Griff. was analysed by capillary gas chromatography and gas chromatography mass spectrometry. The rhizome oil was dominated by sesquiterpenes, the major component being zerumbone, contributing 66.4% of the total oil composition. The rhizome oil and zerumbone, were subsequently evaluated for their anti-amoebic activity against clinical isolate of A. castellanii (ATCC 50492) for the first time. Using amoebicidal assays, the results revealed that essential oil exhibited anti-amoebic effects, exhibiting an IC₅₀ value of 87.67 ± 2.68 µg/mL. Subsequently, Zerumbone was evaluated for its potential anti-amoebic properties and exhibited an IC₅₀ value of 147.95 ± 1.72 µM (32.29 µg/mL). Both zerumbone and the essential oil reduced cyst recovery in encystation experiments and reduced trophozoite recovery in excystation experiments. When tested against human cells, moderate cytotoxicity (up to 40%) against human keratinocyte cells (HaCaT cells) was observed, and higher cytotoxicity at higher concentrations, indicating the need for careful safety and selectivity evaluation. Further studies will determine the underlying molecular mechanisms against various clinical and environmental isolates to establish Zerumbone from Zingiber spectabile Griff. rhizome as promising candidates for further exploration.