BIOSYNTHESIS OF SILVER NANOPARTICLES BY SOILDERIVED Rhizopus arrhizus HGS2I2: ANTIBACTERIAL POTENTIAL AGAINST CARBAPENEM-RESISTANT Escherichia. Coli AND Klebsiella pneumoniae, AND ANTIOXIDANT PROPERTIES

The increase in carbapenem-resistant E. coli and Klebsiella pneumoniae infections presents a serious public health concern due to the scarcity of effective treatment options. This study addresses this challenge by utilizing a green synthesis approach for silver nanoparticles (AgNPs) using the fungal isolate Rhizopus arrhizus HGS2I2. The isolate was confirmed through morphological and molecular techniques, and nanoparticle synthesis was visually verified by a change in solution color. The biogenic synthesized AgNPs are characterized using UV–Vis, dynamic light scattering (DLS), FTIR analysis, and transmission electron microscopy (TEM). The UV–Vis spectrum exhibited a peak around 420 nm, while DLS analysis showed a particle size of approximately 64.23 nm with good uniformity. TEM images revealed a spherical morphology, and FTIR spectra confirmed the presence of functional biomolecules that assist in nanoparticle stabilization. Antibacterial performance of the AgNPs was assessed through the well diffusion assay against drug-resistant isolates of E. coli and K. pneumoniae. The inhibition zones showed a clear concentration-dependent trend. E. coli displayed inhibition zones of 19.66 ± 0.57 mm, 17.0 ± 1.0 mm, and 14.33 ± 0.57 mm, while K. pneumoniae showed zones of 17.33 ± 1.52 mm, 16.33 ± 1.52 mm, and 12.33 ± 2.08 mm at concentrations of 1000, 500, and 250 µg/mL, respectively. Meropenem, used as a control, had no inhibitory effect, confirming resistance. The AgNPs showed potent antibacterial properties, with minimum inhibitory concentrations (MICs) of 10 µg/mL for carbapenem-resistant E. coli and 25 µg/mL for carbapenem-resistant K. pneumoniae. Minimum bactericidal concentrations (MBC) were determined to be 25 µg/mL and 50 µg/mL, respectively. Additionally, antioxidant activity was confirmed via DPPH assay, suggesting the biomedical relevance of the synthesized nanoparticles.