Antibacterial and Antibiofilm Activity of Therapeutic Herbs Stabilized Green Synthesis Silver (Ag) Nanoparticles against Drug Resistant Clinical Pathogen

Different therapeutic herbs are abundantly present in the southern region of Punjab, Pakistan. In the current study, four medicinal herbs, Onosma bracteata Wall., Citrullus colocynthis, Sphaeranthus indicus, and Swertia chirata, were selected for the green synthesis of silver nanoparticles. The synthesized AgNPs were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analysis. SEM analysis showed that the particle size of the synthesized AgNPs was in the range of 75–100 nm, while XRD confirmed a face-centered cubic crystalline structure with an average crystallite size of 24 nm. FTIR analysis indicated the presence of functional groups that may contribute to the reduction, capping, and stabilization of the nanoparticles. The antibacterial and antibiofilm activities of the synthesized AgNPs evaluated against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Ciprofloxacin and linezolid used as standard antibiotics for comparison against E. coli and S. aureus, respectively. Among the four herbal AgNPs, Swertia chirata-derived AgNPs showed the strongest antibacterial activity, with maximum inhibition zones of 42.13 ± 0.17 mm against E. coli and 47.44 ± 0.34 mm against S. aureus at 50 mg/mL. The lowest MIC and MBC values also observed for Swertia chirata AgNPs. Against E. coli, the MIC and MBC were 78.125 µg/mL and 156.25 µg/mL, respectively, while against S. aureus, the MIC and MBC were 39.0625 µg/mL and 78.125 µg/mL, respectively. In the antibiofilm assay, Swertia chirata AgNPs showed the highest biofilm inhibition, reaching 85.77% against E. coli and 71.26% against S. aureus. Phytochemical screening confirmed the presence of bioactive constituents in the herbal extracts, which may have contributed to AgNP synthesis. These findings suggest that green-synthesized herbal AgNPs, particularly those derived from Swertia chirata, have promising antibacterial and antibiofilm potential against drug-resistant bacterial pathogens.