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Plumeria alba (P. alba) is a small laticiferous tree with promising medicinal properties. Green synthesis of nanoparticles is eco-friendly, cost-effective, and non-hazardous compared to chemical and physical synthesis methods. Current research aiming to synthesize silver nanoparticles (AgNPs) from the leaf extract of P. alba (P- AgNPs) has described its physiochemical and pharmacological properties in recognition of its therapeutic potential as an anticancer and antimicrobial agent. These biogenic synthesized P-AgNPs were physiochemically characterized by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscope (TEM), atomic force microscopy (AFM), X-ray diffractometry (XRD), and zeta potential analyses. Antimicrobial activity was investigated against Escherichia coli, Pseudomonas aeruginosa, Enterobacter aerogenes, Enterococcus faecalis, Bacillus subtilis, Streptococcus pneumoniae, Candida albicans, and Candida glabrata. Anticancer activity against glioblasoma U118 MG cancer lines was investigated using an MTT assay, and apoptosis activity was determined by flow cytometry. UV–visible spectroscopic analysis portrayed surface plasmon resonance at 403 nm of synthesized P-AgNPs, and FTIR suggested the presence of amines, alkanes, and phenol molecules that could be involved in reduction and capping processes during AgNPs formation. Synthesized particles were spherical in shape and poly-dispersed with an average particle size of 26.43 nm and a poly-dispersity index (PDI) of 0.25 with a zeta potential value of −24.6 mV, ensuring their stability. The lattice plane values confirm the crystalline nature as identified by XRD. These P-AgNPs exhibited potential antimicrobial activity against selected human pathogenic microbes. Additionally, the in vitro MTT assay results show its effective anticancer activity against the glioma U118 MG cancer cell line with an IC50 value of 9.77 µg/mL AgNPs by initiating apoptosis as identified by a staining study with flow cytometric annexin V–fluorescein isothiocyanate (FITC) and propidium iodide (PI). Thus, P. alba AgNPs can be recommended for further pharmacological and other biological research. To conclude, the current investigation developed an eco-friendly AgNPs synthesis using P. alba leaf extract with potential cytotoxic and antibacterial capacity, which can therefore be recommended as a new strategy to treat different human diseases.

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Background The industrial production of silver nanoparticles (AgNPs) and its commercial applications are being considerably increased in recent times, resulting in the release of AgNPs in the environment and enhanced probability of contaminations and their adverse effects on living systems. Based on this, the present study was conducted to evaluate the in vitro cytotoxicity of actinomycete-synthesized AgNPs on Allium cepa (A. cepa) root tip cells. A green synthesis method was employed for biosynthesis of AgNPs from Streptomyces sp. NS-33. However, morphological, physiological, biochemical, and molecular analysis were carried out to characterize the strain NS-33. Later, the synthesized AgNPs were characterized and antibacterial activity was also carried out against pathogenic bacteria. Finally, cytotoxic activity was evaluated on A. cepa root tip cells. Results Results showed the synthesis of spherical and polydispersed AgNPs with a characteristic UV-visible (UV-Vis.) spectral peak at 397 nm and average size was 32.40 nm. Energy dispersive spectroscopy (EDS) depicted the presence of silver, whereas Fourier transform infrared (FTIR) studies indicated the presence of various functional groups. The phylogenetic relatedness of Streptomyces sp. NS-33 was found with Streptomyces luteosporeus through gene sequencing. A good antibacterial potential of AgNPs was observed against two pathogenic bacteria. Concerning cytotoxicity, a gradually decreased mitotic index (MI) and increased chromosomal aberrations were observed along with the successive increase of AgNPs concentration. Conclusions Therefore, the release of AgNPs into the environment must be prevented, so that it cannot harm plants and other beneficial microorganisms.

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Objective: The present goals of our study were biological synthesis, characterizations of silver nanoparticles, and evaluation of its antimicrobial activity against microbial pathogens like Escherichia coli, Enterococcus faecalis, Streptococcus pneumoniae and Staphylococcus aureus. Methods: The bacterial Strain NS-24 was isolated on nutrient agar medium and was selected for the synthesis of silver nanoparticles based on its gram-negative characteristics. The characterizations of silver nanoparticles were done by UV-Visible spectroscopy, Atomic Force Microscopy (AFM), High Resolution-Transmission Electron Microscopy (HR-TEM), Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDX), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Later, the molecular characterization of the Strain NS-24 was done by DNA extraction and 16S rRNA gene sequencing. Results: The UV-visible spectrophotometric observation of the Strain NS-24 supernatant and AgNO3 solution showed maximum absorbance at 423 nm. The AFM data confirmed that the particles were polydispersed and spherical in shape. Additionally, the FTIR analysis revealed the IR spectral band patterning and TEM analyzes showed the size of biological AgNPs was in the range of 12.56 nm to 27.32 nm, with an average of 18.06 nm in size. Further, the 16S rRNA gene sequencing revealed the identity of Strain NS-24 as Stenotrophomonas maltophilia. The antimicrobial activity of AgNPs was studied on different gram-negative and gram-positive bacterial strains like Escherichia coli (MTCC 40), Enterococcus faecalis (MTCC 6845), Streptococcus pneumoniae (MTCC 8874) and Staphylococcus aureus (MTCC 2825), which showed good inhibition of their growth at varying concentrations of AgNPs against all the pathogens. Conclusion: Our findings showed that the synthesized AgNPs from the isolated bacterium was small in size and had profound antibacterial activity against pathogenic micro-organisms.

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