Unveiling the antibacterial potential of Arctotis aurantiaca roots: isolation, characterization, and computational studies

Phytochemical investigation of the total ethanolic extract and various derived fractions of Arctotis aurantiaca roots resulted in the isolation of eight chemically diverse metabolites, including two fatty alcohols [n-octacosanol (1) and n-pentacosanol (2)], three sesquiterpene lactones [9β‑hydroxy-11 β,13-dihydrozaluzanin C (3), 11α, 13-dihydroglucozaluzanin C (5), and ixerin F (6)], one coumarin [6-Methoxy-7-hydroxycoumarin (scopoletin) (4)], one lignan [4,8-dimethoxyeudesmin (7)] and one phenolic acid derivative [3,5-dicaffeoylquinic acid methyl ester (8)] using different chromatographic techniques. The antibacterial activity of these isolated compounds was investigated against Escherichia coli ATCC 25,922 using well-diffusion assay technique. Among the tested compounds, compound (6) exhibited the strongest antibacterial activity with a MIC of 1.7 µg/mL, whereas compound (1) was the least potent with a MIC of 218.2 µg/mL compared to gentamicin (MIC= 2 µg/mL) as a positive control. Additionally, molecular docking and 140 ns molecular dynamics (MD) simulations were performed to evaluate the binding interactions of the isolated compounds with E. coli DNA gyrase A. The results indicated that ixerin F (6) showed strong binding affinity and stability over 140-nanosecond simulation, highlighting its potential as an antibacterial agent. This study underscores the integration of computational and experimental methods to develop novel antibacterial strategies against E. coli, presenting A. aurantiaca as a candidate antibacterial plant by targeting bacterial DNA gyrase, a key enzyme involved in regulating DNA topology and supercoiling, which indirectly impacts essential cellular processes such as replication and transcription.