In Vitro Screening of Butcher’s Broom (Ruscus aculeatus L.) Cladodes and Aerial Parts Extracts Against Fish Pathogen Isolates

The growing need for sustainable alternatives to antibiotics in aquaculture has increased interest in plant-derived antimicrobial compounds. This study characterized ethanol and methanol extracts from the cladodes and aerial parts of butcher’s broom (Ruscus aculeatus L.) by GC–MS and screened, as a preliminary in vitro assessment, their antibacterial activity against Aeromonas hydrophila, Lactococcus garvieae, Vibrio anguillarum, Edwardsiella tarda, and Yersinia ruckeri. The extracts showed distinct chemical profiles. Phytol showed the highest relative chromatographic abundance in the ethanol cladode extract (25.16% of the total ion chromatogram peak area), whereas n-hexadecanoic acid dominated the ethanol aerial parts extract (42.08%). In the methanol cladode extract, the most abundant peak was a co-eluting group (2,2-dimethylbutane/1,2-dimethylaziridine/oxalic acid isobutyl pentyl ester; 22.21%), followed by methyl 9,12,15-octadecatrienoate (14.64%) and phytol (7.86%), while the methanol aerial parts extract was characterized by a 4H-pyran-4-one derivative (16.41%). Antibacterial activity varied with extract, pathogen, and dose, with maximum inhibition zones of 25.0 ± 1.0 mm against A. hydrophila, 24.0 ± 1.0 mm against Y. ruckeri, and 23.7 ± 0.6 mm against V. anguillarum. The E. tarda isolate was the least susceptible. These preliminary findings provide the first evidence of antibacterial activity of R. aculeatus extracts against fish pathogens and support further investigation of this species as a potential source of antimicrobial phytochemicals for aquaculture.