AccScience Publishing / IMO / Online First / DOI: 10.36922/IMO025310036
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ORIGINAL RESEARCH ARTICLE

Antibacterial potential, phytochemical constituents, and toxicity assessment of Azadirachta indica leaf extracts in combination with antibiotics

Gagan Tiwana1 ,  Ian Edwin Cock2,3 ,  Matthew James Cheesman1*
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1 School of Pharmacy and Medical Sciences, Gold Coast Campus, Griffith University, Parklands Drive, Southport, Queensland, Australia
2 School of Environment and Science, Nathan Campus, Griffith University, Nathan, Queensland, Australia
3 Environmental Futures Research Institute, Nathan Campus, Griffith University, Nathan, Queensland, Australia
IMO, 025310036 https://doi.org/10.36922/IMO025310036
Received: 30 July 2025 | Revised: 22 September 2025 | Accepted: 10 October 2025 | Published online: 28 November 2025
© 2025 by the Author(s). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution -Noncommercial 4.0 International License (CC-by the license) ( https://creativecommons.org/licenses/by-nc/4.0/ )
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Abstract

The rise of antimicrobial resistance (AMR) has highlighted the need for exploration of alternative therapeutic agents, including medicinal plants. This study investigates the antibacterial potential, phytochemical composition, and toxicity of Azadirachta indica leaf extracts, along with their interactions with conventional antibiotics. Extracts prepared in water (AQ), methanol (MeOH), and ethyl acetate (EtOAc) were evaluated for growth-inhibitory effects against a range of bacterial species, including drug-resistant isolates, through both disc diffusion and microdilution methods. Zone of inhibition (ZOI) measurements ranged from 7 to 10 mm, while minimum inhibitory concentration values varied between 2938 and 5875 μg/mL for AQ extracts, and between 1175 and 4700 μg/mL for MeOH extracts. Notably, EtOAc extracts did not inhibit bacterial growth in either assay. Fractional inhibitory concentration (FIC) analysis revealed additive interactions of extracts with β-lactam antibiotics (penicillin G, oxacillin, amoxicillin) and protein synthesis inhibitors (tetracycline, chloramphenicol), particularly against Bacillus cereus, Staphylococcus aureus, and Shigella spp., suggesting a potential role as antibiotic adjuvants. However, antagonistic interactions were also observed in combinations containing gentamicin and polymyxin B. Liquid chromatography–mass spectrometry (LC-MS) analysis confirmed the presence of phytochemicals, including flavonoids, tannins, and phenolics, which are known for their antimicrobial properties. Evaluation of extract safety using brine shrimp (Artemia franciscana) assays revealed no toxic responses. To ensure their safety for therapeutic applications, future toxicity evaluations should be conducted on mammalian cell lines to confirm these findings. Future research should focus on isolating bioactive compounds from the extracts, elucidating their mechanisms of action, and optimizing extract-antibiotic formulations to combat resistant bacterial infections effectively.

Graphical abstract
Keywords
Phytochemicals
Medicinal plants
Antibiotic combinations
Natural antibacterial agents
LC-MS profiling
Funding
None.
Conflict of interest
The authors declare that they have no competing interests.
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Innovative Medicines & Omics, Electronic ISSN: 3060-8740 Print ISSN: 3060-8910, Published by AccScience Publishing
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