Green synthesis, characterisation and antibacterial activities of Strobilanthes crispus-mediated silver nanoparticles (SC-AGNPS) against selected bacteria

This study aims to characterize and determine the antibacterial activities of synthesized Strobilanthescrispus-mediated AgNPs (SC-AgNPs) against Streptococcus mutans, Escherichia coli and Pseudomonas aer-uginosa. S. crispus water extract acts as a reducing and capping agent in the synthesis of AgNPs. Thesynthesized AgNPs were characterized by using UV-Vis spectrophotometer, dynamic light scattering(DLS), field emission scanning electron microscope (FESEM), X-ray diffractometer (XRD) and Fouriertransform infra-red (FTIR). FESEM images showed a rough surface with a spherical shape. The averagesize distribution of 75.25 nm with a polydispersity index (PDI) of 0.373. XRD analysis matched the face-centred cubic structure of silver. FTIR analysis revealed a shifted peak from 1404.99 to 1345.00 cm−1.MIC and MBC values of SC-AgNPs were 1.25 mg/mL and 2.5 mg/mL against E. coli, P. aeruginosa andS. mutans, respectively. Time-kill assay showed that SC-AgNPs significantly reduced bacterial growth ascompared to non-treated bacteria. Morphologies of bacteria treated with SC-AgNPs were shrunk, lysed,irregular and smaller as compared to control. SC-AgNPs significantly disrupted the gene expression ofeae A, gtf B and Pel A (p < 0.05). This study indicated that the synthesized SC-AgNPs were stable withenhanced antibacterial activities.