Microbial infections remain public health problems because of the upsurge of bacterial resistance. The present study aimed to evaluate the anti-quorum sensing, antimicrobial activities, and chemical compositions of Acacia macrostachya. Total phenolic, flavonoid, and condensed tannin content were determined according to Folin–Ciocalteu, aluminum chloride, and Broadhurst methods, respectively. The microdilution method using p-iodonitrothétrazolium was used to evaluate the antibacterial activity. Inhibition of pyocyanin and violacein production by extract and fraction was used to evaluate anti-quorum sensing activity. The antioxidant activity was evaluated using 2,2-diphenyl-1-picryl-hydrazyl, Ferric reducing, and hydrogen peroxide scavenging methods. The minimum inhibitory concentration of the extracts and fractions ranged from 0.312 to 5 mg/ml. At 100 µg/ml, ethyl acetate fraction significantly inhibited the production of violacein (56.45%) and pyocyanin (48.88%). The total phenolic, flavonoids, and condensed tannin contents ranged from 31.85 ± 0.31 to 21.26 ± 0.67 mg gallic acid equivalent (GAE)/100 mg, 26.35 ± 0.71 to 25.42 ± 0.36 mg quercetin equivalent (QE)/100 mg, and 18.24 ± 0.12 to 15.9 ± 0.17 mg Catechin equivalent (CE)/100 mg, respectively. The antioxidant activity correlates with phenolic, flavonoids, and tannin contents. High Pressure Liquide Chromatography (HPLC) analysis of the ethyl acetate fraction allowed to identify three phenolic acids and five flavonoids. The results described here could justify the use of A. macrostachya by traditional healers to treat infections, and particularly, gastrointestinal disorders

Acacia macrostachya, antioxidant, antibacterial