Activity of essential oils against Caenorhabditis elegans: Showing anthelmintic potential for new products

The emergence of anthelmintic resistance in livestock and companion animal parasites necessitates the search for alternative therapeutic molecules. This study investigated the nematicidal activities of six essential oils (EOs) - Thymus vulgaris, Eugenia caryophyllus, Cymbopogon flexuosus, Illicium verum, Pelargonium graveolens, and Origanum vulgare - using Caenorhabditis elegans as a model organism. Methods included adult lethality, egg hatching, and egg-laying assays, as well as scanning electron microscopy (SEM) to assess cuticular damage. Strains tested included the wild-type (N2) and four resistant strains (ivermectin, benzimidazole, levamisole, and organophosphate). Chemical characterization via GC-MS identified major constituents, including carvacrol (58.92%) in O. vulgare and eugenol (76.84%) in E. caryophyllus. In lethality assays, O. vulgare exhibited the highest potency against adults (LC₅₀ 1.03 µg.mL⁻¹) and eggs (LC₅₀ 13.70 µg.mL⁻¹). The P. graveolens also demonstrated significant ovicidal activity (LC₅₀ 16.20 µg.mL⁻¹). The I. verum (RR=1.1) and T. vulgaris (RR=0.8) maintained efficacy against ivermectin resistant strains, while T.vulgaris (RR=0.7) and P. graveolens (RR=1.4) showed efficacy against albendazole. These low Resistance Ratios (RR < 2) indicate a lack of cross-resistance and highlight the potential of these essential oils against multidrug-resistant nematode populations. Egg-laying was significantly inhibited at sub-lethal concentrations across 5 of 6 tested oils. SEM analysis revealed substantial morphological alterations, including cuticle wrinkling and degradation, suggesting a primary mechanism of action involving integumentary disruption. These findings highlight O. vulgare and I. verum as promising candidates for developing new anthelmintic products. The use of C. elegans proved to be a preliminary screening tool for identifying bioactive compounds with broad-spectrum potential.