Phytochemical Profiling and Antimicrobial Evaluation of Olea europaea Leaf Extracts: Unravelling the Superior Activity of Dichloromethane Fraction from a Nigerian Chemotype

Abstract

The escalating crisis of antimicrobial resistance has intensified the search for plant-derived therapeutic alternatives. This study investigated the phytochemical composition and antimicrobial potential of sequentially extracted fractions (n-hexane, dichloromethane, ethyl acetate, and methanol) from Olea europaea leaves collected in Katsina State, Nigeria, against clinically relevant bacterial pathogens. Phytochemical screening revealed steroids, alkaloids, and terpenoids uniformly present across all fractions, while flavonoids were conspicuously absent—challenging conventional assumptions. Antimicrobial evaluation demonstrated that the dichloromethane fraction exhibited the broadest and most potent activity, with inhibition zones reaching 22 mm against Bacillus spp. and 19 mm against Staphylococcus aureus, retaining activity against Pseudomonas spp. down to 50 mg/mL. The ethyl acetate fraction showed notable activity against Salmonella spp. (22 mm), while methanol extracts displayed comparatively weak activity, contrary to previous reports favoring polar solvents. Gas Chromatography-Mass Spectrometry of the ethyl acetate fraction identified 35 compounds, with dominant constituents including 1-nonadecene (28.41%), 1-heptadecene (17.64%), 1-pentadecene (13.32%), and bioactive markers such as 2,4-di-tert-butylphenol, n-hexadecanoic acid, caryophyllene oxide, and squalene. This first comprehensive profiling of Nigerian-grown Olea europaea establishes that the dichloromethane fraction—rather than the conventionally favored methanol fraction- yields superior antibacterial activity. The findings highlight olive leaves as a promising source of natural antimicrobial agents, warranting further bioassay-guided fractionation for novel compound discovery.