Medicinal Plant Extracts as Potential β-Lactamase Inhibitors: Integrated Evaluation of β-Lactamase Enzyme Inhibition and in vitro Cytotoxicity

Background: The increasing prevalence of β-lactamase-mediated antimicrobial resistance has substantially reduced the effectiveness of β-lactam antibiotics, highlighting the need to identify novel β-lactamase inhibitors. Medicinal plants are rich sources of structurally diverse phytochemicals and represent promising candidates for the discovery of natural antibiotic adjuvants capable of overcoming bacterial resistance mechanisms. Aim: This study aimed to evaluate the β-lactamase inhibitory activity and in vitro cytotoxicity of selected medicinal plant extracts to identify promising candidates for subsequent phytochemical investigation. Materials and Methods: Aqueous, methanolic, and ethyl acetate extracts prepared from Azadirachta indica A. Juss., Phyllanthus emblica Linn., Phyllanthus niruri Linn., Ocimum tenuiflorum Linn., Solanum nigrum Linn., Terminalia bellirica Gaertn. Roxb., and Terminalia chebula Retz. were screened for β-lactamase inhibitory activity using a commercial kit of β-lactamase enzyme assay. Cytotoxicity was assessed against human dermal fibroblast adult (HDF-a) cells using a resazurin-based cell viability assay. The findings were subsequently interpreted in the context of LC-MS-guided phytochemical investigations. Results: Methanolic extracts of A. indica and P. emblica exhibited the greatest β-lactamase inhibitory activity, whereas T. bellirica demonstrated little or no detectable inhibition. All extracts except the methanolic extract of S. nigrum were non-toxic toward HDF-a cells at 300 µg/mL. Conclusion: The selected medicinal plant extracts possess β-lactamase inhibitory activity under the experimental conditions evaluated. These findings identify medicinal plant extracts as potential sources of bioactive compounds capable of targeting β-lactamase-mediated antimicrobial resistance and provide a strong foundation for subsequent phytochemical isolation, functional characterisation, and validation of individual β-lactamase inhibitors. Collectively, this work supports the continued exploration of plant-derived natural products as antibiotic adjuvants to restore the efficacy of β-lactam antibiotics against resistant bacterial pathogens.