Biogenic synthesis of silver nanoparticles using cell-free extract of Bacillus safensis LAU 13: antimicrobial, free radical scavenging and larvicidal activities

The cell-free extract of Bacillus safensis LAU 13 strain (GenBank accession No: KJ461434) was used for green biosynthesis of silver nanoparticles (Ag-NPₛ). Characterization of Ag-NPₛ was carried out using UV-VIS spectroscopy, Fourier-transform infrared spectroscopy, and transmission electron microscopy. Evaluation of synthesized Ag-NPs as antimicrobial agents was done using multi-drug resistant clinical isolates as well as their synergistic effects when combined with some selected antibiotics. Furthermore, potential of Ag-NPₛ as antimicrobial additives in paint was demonstrated. The Ag-NPₛ have maximum absorbance at 419 nm, with peaks at 3308, 2359, 1636, and 422 cm⁻¹, indicating that proteins were the capping and stabilisation molecules in the synthesis of Ag-NPₛ. The particles were spherical shaped having size of 5-95 nm, with silver as the prominent metal from the energy dispersive X-ray analysis, while selected area electron diffraction pattern agrees well with the crystalline nature and face-centred cubic phase of Ag-NPs. Inhibition of Staphylococcus aureus, Escherichia coli, Klebsiella granulomatis and Pseudomonas aeruginosa was achieved at 100 μg/mL. Improvement of activities of augmentin, ofloxacin and cefixime to the tune of 7.4-142.9% was achieved in synergistic study, while total inhibitions of P. aeruginosa, S. aureus, Aspergillus flavus and Aspergillus fumigatus were achieved in Ag-NPₛ-paint admixture. The Ag-NPₛ showed potent antioxidant and larvicidal activities with IC₠₀ and LC₠₀ of 15.99 and 42.19 μg/mL, respectively. The present study demonstrated that the biosynthesized Ag-NPs have potent biological activities, which can find applications in diverse areas. The report adds to the growing biotechnological relevance of B. safensis.