Chemical Characterization and Evaluation of the Antimicrobial Properties of Leaf Extracts from Five Ethnomedicinal Plants in Paschim Medinipur District, West Bengal, India

This study examines the physicochemical properties, phytochemical composition, and antimicrobial potential of five medicinal plants—Acalypha indica, Senna tora, Euphorbia hirta, Physalis angulata, and Ziziphus mauritiana—traditionally used in folk medicine. Fresh leaves were collected from Paschim Medinipur district, West Bengal, India and subjected to proximate and ultimate analyses, Fourier-transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC-MS), and antimicrobial assays against Escherichia coli and Staphylococcus aureus. Results revealed that Acalypha indica exhibited the highest levels of volatile matter (75.452%), cellulose (61.727%), and tannins (0.635 g/100g), indicating a rich phytochemical profile. Physalis angulata recorded the highest fixed carbon (15.251%) and extractive content (1.974%), while Senna tora showed elevated ash (12.327%) and lignin content (5.531%). Euphorbia hirta had the highest carbohydrate (9.619 g/100g) and nitrogen content (2.050%) and Ziziphus mauritiana displayed the highest protein (2.321 g/100g), fat (0.655 g/100g) and oxygen content (34.222%). FTIR confirmed the presence of key functional groups, and GC-MS identified 10 bioactive compounds in A. indica and S. tora and 8 in the remaining plants. Several compounds, such as Cyclotrisiloxane, Myo-Inositol, and 4-Tert-Octylphenol, lacked prior records of individual bioactivity and are considered novel, warranting further investigation. Antimicrobial tests showed strong activity against Staphylococcus aureus, a Gram-positive bacterium, but no inhibition of Escherichia coli, likely due to its outer lipopolysaccharide membrane acting as a barrier to bioactive compounds. The results of this study demonstrate that plant extracts from Acalypha indica, Senna tora, Physalis angulata, Euphorbia hirta and Ziziphus mauritiana exhibit significant antibacterial activity against Staphylococcus aureus, a Gram-positive bacterium, while showing no inhibitory effect against Escherichia coli, a Gram-negative bacterium. The susceptibility of S. aureus to plant extracts, as indicated by the MIC, MBC, and DAD assays, strongly suggests that these extracts contain bioactive compounds capable of penetrating and disrupting bacterial cell structures. However, the absence of antimicrobial activity against E. coli supports the well-established concept that Gram-negative bacteria have an outer membrane composed of lipopolysaccharides (LPS), which acts as a selective permeability barrier, preventing many antimicrobial agents from entering the cell. The study validates the traditional medicinal use of these plants and highlights their potential as sources of novel antibacterial agents and phytopharmaceuticals.