Characterization of Silver Nanoparticles Biosynthesized using Keratinase from Aspergillus species and their Antibacterial Activity against Clinical Pathogens

Silver nanoparticle (AgNP) synthesis using biologically sourced agents has recently gained interest from researchers due to its environmentally friendly, cost-effective and non-toxic nature. This study evaluated the antibacterial potential of AgNPs biosynthesized using crude keratinase produced by Aspergillus recovered from dumpsite. Aspergillus species were cultured in a minimal medium containing feather (1%) and yeast extract (0.2%) for the bioproduction of keratinase. Silver nitrate (1 mM) was bio-reduced using keratinase and characterized using UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). The antibacterial potentials of the AgNPs were investigated on multidrug resistant-clinical pathogens (Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Yersinia enterica, Klebsiella pneumoniae, Serratia liquefaciens, Citrobacter freundii, Enterobacter cloacae and Klebsiella oxytoca) using disk diffusion method. Three fungal isolates A. niger (F1), A. oryzae (F2) and A. aculeatus (F3) were recovered with A. niger (F1) and A. aculeatus (F3) showing high keratinase activities of 48.52 U/ml and 46.04 U/ml, respectively. Absorbance peaks of 289 nm and 295 nm were observed for A. niger (AgNPs-F1) and A. aculeatus (AgNPs-F3), respectively. The spectral peaks from the FTIR revealed the presence of O-H stretch of amide (3616.59 and 3474.41) in biosynthesized AgNPs. Particle sizes ranging from 3.04 to 12.39 nm and 15.47 to 32.83 nm were observed for AgNPs-F1 and AgNPs-F3, respectively. AgNPs-F1 and AgNPs-F3 showed antibacterial against 80% and 70% of test isolates with Staphylococcus aureus, Yersinia enterica, Klebsiella pneumoniae, Enterobacter cloacae and Klebsiella oxytoca as the most susceptible pathogens.