Phytochemical Profiling, Antioxidant, Antimicrobial and Cytotoxic Activities of Stipagrostis plumosa (Poaceae): Potential Implications for Human and Veterinary Health.

Stipagrostis plumosa is a desert grass that remains relatively underexplored with respect to its phytochemical composition and biological activities, particularly against pathogens of veterinary relevance. This study aimed to characterize the phytochemical profile of S. plumosa and evaluate the antioxidant, antimicrobial, and cytotoxic activities of its extracts and solvent fractions. Aerial parts of S. plumosa were collected during the flowering season from Al-Quwai'iyah, Saudi Arabia, and subjected to methanolic extraction followed by solvent fractionation. Total phenolic and flavonoid contents, antioxidant activity, antimicrobial activity against bacterial and fungal strains, and cytotoxicity against MCF-7 and A549 cells were evaluated. GC-MS was used to characterize the ethyl acetate and chloroform fractions. The crude methanolic extract contained 72.1 mg GAE/g extract of total phenolics and 13.6 mg QE/g extract of total flavonoids. The ethyl acetate fraction exhibited the strongest antioxidant activity (IC50 = 72.48 µg/mL) and the most pronounced antimicrobial activity, whereas the chloroform fraction showed the highest cytotoxic activity against MCF-7 and A549 cells, with IC50 values of 173.52 and 194.17 µg/mL, respectively. GC-MS profiling revealed diverse phenolic derivatives, fatty acids and their esters, oxygenated compounds, and phytosterol-related constituents. Stigmasta-3,5-dien-7-one (14.70%) and vanillic acid (7.18%) predominated in the ethyl acetate fraction, while hexadecanoic acid methyl ester (5.28%) was among the major constituents of the chloroform fraction. Overall, the fraction-dependent biological activities and diverse phytochemical profiles highlight S. plumosa as a promising source of natural bioactive compounds with potential relevance to veterinary health and the development of alternative antimicrobial strategies.