Research Article | Volume: 15, Issue: 7, July, 2025

Boosting amoxicillin effectiveness against methicillin-resistant Staphylococcus aureus and ancomycin-resistant Enterococcus faecalis with phytochemicals: In vitro and in silico approaches

Pannapa Powthong,  Nonthalert Lertnitikul,  Cherdsak Boonyong   

Pannapa Powthong1, Nonthalert Lertnitikul2,3, Cherdsak Boonyong4

1Microbiology Unit, Department of Medical Sciences, Faculty of Science, Rangsit University, Pathum Thani, Thailand.

2Department of Pharmacognosy and Pharmaceutical Botany, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, Thailand.

3Animal Models of Chronic Inflammation-Associated Diseases for Drug Discovery Research Unit, Chulalongkorn University, Bangkok, Thailand.

4Pharmacology and Toxicology Unit, Department of Medical Sciences, Faculty of Science, Rangsit University, Pathum Thani, Thailand.

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Published:  Jun 05, 2025

DOI: 10.7324/JAPS.2025.229288
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Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecalis (VRE) are one of the significant public health issues. They are associated with high rates of illness and death, and increased prevalence of antimicrobial resistance, which causes treatment failure in infectious diseases. This study investigated the effects of combined seven phytochemicals, including four stilbenoids [namely, pinosylvin monomethyl ether (1), 2,3’-dihydroxy-5’-methoxystilbene (2), (E)-2,3′-dihydroxy-2′-(4-hydroxybenzyl)-5′-methoxystilbene (3), (E)-2,5′-dihydroxy-2′-(4-hydroxybenzyl)-3′-methoxystilbene (4)], one flavonoid (isalpinin) (5), one triterpenoid saponin (oleanolic acid 28-O-β-D-glucopyranoside) (6), and one amide alkaloid (piperine) (7) with amoxicillin and predicting mode of action of seven natural compounds with amoxicillin to kill MRSA and VRE. The antibacterial activity was assessed by the minimum inhibitory concentration (MIC) and fractional inhibitory concentration (FIC) index. In addition, a molecular docking study was evaluated to predict the mechanism of action of their compounds to bind resistance-related proteins: penicillin-binding protein 2a (PBP2a) for MRSA and VanA ligase for VRE. All compounds showed antibacterial activity (MIC: 5–10 mg/ml) and enhanced amoxicillin efficacy, with FIC index values indicating additive to synergistic effects (FIC: 0.0018–0.8020). The compounds interacted with PBP2a at allosteric sites (ΔG: –11.70 to –6.60 kcal/mol; Ki: 0.00263–14.65 μM) and with VanA ligase at active sites (ΔG: –10.46 to –7.20 kcal/mol; Ki: 0.021–5.32 μM), exhibiting favourable binding affinities. In contrast, amoxicillin showed unfavourable interactions with these proteins. This study suggests that compounds 1–7 increased the susceptibility of MRSA and VRE to amoxicillin, which might be associated with their interaction with PBP2a and VanA proteins.


Keyword:     Methicillin-resistant Staphylococcus aureus vancomycin-resistant Enterococcus faecalis antibacterial activity penicillin-binding protein 2a VanA ligase amoxicillin phytochemical

Citation:

Powthong P, Lertnitikul N, Boonyong C. Boosting amoxicillin effectiveness against methicillin-resistant Staphylococcus aureus and ancomycin-resistant Enterococcus faecalis with phytochemicals: In vitro and in silico approaches. J Appl Pharm Sci. 2025;15(07):121–131. https://doi.org/10.7324/JAPS.2025.229288

Copyright: © The Author(s). This is an open-access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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