Characterization and antibacterial activity of silver nanoparticles synthesized by soil-dwelling Bacillus thuringiensis against drug-resistant bacteria

Alternative antibacterial options and nanotechnology have gained attention as a solution to the current antibiotic resistance crisis. The use of microorganisms to synthesize nanoparticles is applauded as a sustainable alternative for the production of metal-based nanoparticles. This research screened Bacillus thuringiensis (Bt) isolated from soils collected from different sites (farmland, cattle rangeland and metal recycling dumpsite) for their silver nanoparticles (AgNPs) synthesis potential, characterised the AgNPs and assessed their antibacterial activity against selected drug-resistant bacteria. The Bt index of the sampled sites ranged from 0.1 (farmland) to 0.5 (cattle rangeland). Out of six confirmed Bt isolates; MRS2(1) and CR2(3) were selected for their AgNP synthesis potential based on their absorbance of AgNPs at 420 nm. Both isolates produced AgNPs which were anistropic and irregular in shape. The surface plasmon resonance of silver occurred at 434.5 and 440 nm with distinct FT-IR peaks at 3379 and 1643 cm(- 1). Apart from the multidrug-resistant E. coli (strain 1), the AgNPs from the two selected isolates exhibited antibacterial activity against E. coli (strain 2), S. aureus and K. pneumoniae. Antibacterial activity of the AgNPs was achieved at 25 mu g/mL with MIC of 25-50 mu g/mL and MBC of 75-100 mu g/mL. Further studies are required to assess the effect of environmental factors on the properties of AgNPs synthesized, their mechanism of antibacterial activity and, synergistic effect of AgNP and antibiotics.