Antibacterial, Antibiofilm, and Efflux Pump Inhibitory Properties of the Crude Extract and Fractions from Acacia macrostachya Stem Bark

Abstract

Microbial infections remain a public health problem due to the upsurge of bacterial resistance. In this study, the antibacterial, antibiofilm, and efflux pump inhibitory activities of the stem bark of Acacia macrostachya, an indigenous African medicinal plant, were investigated. In traditional medicine, the plant is used in the treatment of microbial infections and inflammatory conditions. A crude methanol extract obtained by Soxhlet extraction was partitioned by column chromatography to obtain the petroleum ether, ethyl acetate, and methanol fractions. Antibacterial, efflux pump inhibition and antibiofilm formation activities were assessed by the high-throughput spot culture growth inhibition (HT-SPOTi), ethidium bromide accumulation, and the crystal violet retention assay, respectively. The minimum inhibitory concentrations (MICs) of the crude extract and major fractions ranged from 250 to ≥500 μg/mL. At a concentration of 3.9–250 μg/mL, all extracts demonstrated >80% inhibition of biofilm formation in S. aureus. In P. aeruginosa, the EtOAc fraction showed the highest antibiofilm activity (59–69%) while the pet-ether fraction was most active against E. coli biofilms (45–67%). Among the test samples, the crude extract, methanol, and ethyl acetate fractions showed remarkable efflux pump inhibition in S. aureus, E. coli, and P. aeruginosa. At ½ MIC, the methanol fraction demonstrated significant accumulation of EtBr in E. coli having superior efflux inhibition over the standard EPIs: chlorpromazine and verapamil. Tannins, flavonoids, triterpenoids, phytosterols, coumarins, and saponins were identified in preliminary phytochemical studies. Stigmasterol was identified in the EtOAc fraction. This study justifies the use of A. macrostachya in the treatment of infections in traditional medicine and highlights its potential as a source of bioactive compounds that could possibly interact with some resistance mechanisms in bacteria to combat antimicrobial resistance.

Staphylococcus aureus biofilm: Formulation, regulatory, and emerging natural products-derived therapeutics

“… Source Extract Strain MIC ( μ g/mL) Biofilm formation inhibition Mature biofilm disruption Target In vivo Ref. Acacia macrostachya Stem barks, MeOH S. aureus >500 >60 %, 3.9 μg/mL NS QS N [ 118 ] Allium subhirsutum Bulbs, H 2 O S. aureus 10000 56.21 %, 10 mg/mL NS QS N [ 116 ] Aphanamixis polystachya Leaves, DCM, MeOH MRSA 6700 >40 %, 125 μg/mL >20 %, 125 μg/mL NS N [ 115 ] Artocarpus heterophyllus Heartwood, EtOH MRSA 31.2–62.5 60 %, 31.2 μg/mL NS NS N [ 134 ] Azadirachta indica Leaves, EtOH MRSA 1000 78.2–91.8 %, 1∼32 mg/mL NS NS N [ 113 ] Capsicum annuum Fruits, MeOH S. aureus …”

“…In particular, 5-hydroxymethylfurfural at 125 μg/mL have been previously reported to inhibit the S. aureus biofilm formation by 82 %, which might be the contributing component of A. subhirsutum [ 117 ]. The possible quenching of QS mechanism was also demonstrated in the crude extract of Acacia macrostachya [ 118 ]. In addition, the methanolic extract of Illicium verum showed a biofilm inhibition effect with 3-hydroxybenzoic acid (3-HBA) as the primary active constituent, which strongly interacted with the active site residues of SarA and AgrA of S. aureus [ 119 ].…”

Magnolia officinalis L. bark extract and respiratory diseases: From traditional Chinese medicine to western medicine via network target

“…The calcium channel antagonist effect is particularly important as it is synergistic against fungi (Marangoni et al, 2017) and against bacteria ( Barfour et al, 2021): Ca 2+ and Mg 2+ , two alkaline-earth-metal ions physiologically essential for diverse living organisms, both disrupt model of S. aureus membranes and kill stationary-phase S. aureus cells, indicative of membrane-activity (Xie & Yang, 2016). Effects on calcium channels are also reflected in spontaneous motility.…”