Study of Ageratum conyzoides L. (Asteraceae) Phytochemical Composition as Quorum-sensing Inhibitors to Combat Antibiotic-resistant Bacterial Infections

The rise of antibiotic-resistant bacterial infections has intensified the search for plant-derived quorum-sensing (QS) inhibitors as alternative therapeutic strategies. Ageratum conyzoides L. has a long history of traditional use as an antimicrobial agent against multidrug-resistant pathogens, yet the phytochemical basis of its QS-inhibitory activity remains incompletely characterized. This study aimed to investigate the phytochemical composition of A. conyzoides and evaluate its potential as a QS inhibitor and antioxidant. Bioassay-guided fractionation of the methanol extract was conducted using flash chromatography on a C18 column. High-performance thin-layer chromatography (HPTLC) was used to establish the phytochemical profile of active subfractions. Antioxidant activity was assessed using the DPPH radical scavenging, ferric reducing antioxidant power (FRAP), and ABTS Trolox equivalent antioxidant capacity assays. QS inhibition was evaluated by measuring violacein production in Chromobacterium violaceum CV026 and pyocyanin production in Pseudomonas aeruginosa PAO1. Fractionation identified subfraction F2-5-3 as an effective inhibitor of both violacein and pyocyanin production. HPTLC analysis revealed the presence of phenolic acids and flavonoids in this fraction, with total phenolic and flavonoid contents of 99.94 ± 0.04 mg/g gallic acid equivalent (GAE) and 16.82 ± 0.21 mg/g quercetin equivalent (QE), respectively. The fraction also demonstrated significant iron reduction capacity, ABTS scavenging activity, and a DPPH IC₅₀ of 14.36 ± 3.76 µg/mL. These findings provide scientific validation for the traditional use of A. conyzoides and support its potential as a promising source of QS-inhibiting phytochemicals for combating antibiotic-resistant infections.