Mountain Top University Library

Biogenic synthesis of silver nanoparticles is a promising method to supplement antibioticaction or completely replace the role of antibiotics due to its biotic nature when compared to physical and chemical methods of producing silver nanoparticles. This study is aimed at isolating, screening, and synthesizing silver nanoparticles using bacterial isolate. Soil samples were collected, cultured, and screened for antibiotics production. The best isolate was identified using morphological, biochemical, and molecular characterizations. Functional
characterizations of the biosynthesized silver nanoparticles (AgNPs) was carried out using visual observation, UV-spectrophotometer, FT-IR, SEM, TEM, XRD, EDX, TGA, and AFM analysis were investigated. The produced AgNPs were used as an antibacterial agent against Enterotoxigenic Escherichia coli, Staphylococcus aureus, Proteus mirabilis, Salmonella enterica serotype I, and Enterococcus faecalis. Out of the 262 bacterial isolates, only five possessed antibacterial activities, out of which, isolate OPG3 was able to biosynthesize AgNO3 which was identified as Bacillus subtilis-OPG3 strain. Colour change from yellow to dark brown, was monitored at an absorbance spectrum between 200 nm to 800 nm
wavelengths between 24 to 72 hours. Moreover, FT-IR spectra showed 15 peaks with ten functional groups which contributed to the synthesized Bacillus subtilis nanoparticles (BSNPs) and SEM micrograph showed aggregated crystals of 7.3 nm, 8.3 nm and 8.5 nm, while TEM showed uniform spherical shapes. The XRD pattern showed four notable peaks at 2θ values. EDX analysis revealed silver to be the major elemental component of BSNPs at 77.20%. TGA profile showed a continuous weight loss with two sharp quasi-sharp changes occurring at 99.9oC and 394oC, and AFM analysis portrayed white patches with spherical
forms. The biosynthesized BSNPs showed improved inhibitory effect (P≥0.05) when compared to the bacterial extract, and streptomycin antibiotics against S. enterica serotype I (32.75±0.41a , 22.50±0.33b and 13.0±0.11c mm), S. aureus (24.75±0.31a
, 14.50±0.21b and 15.0±0.15b mm), Enterotoxigenic E. coli (22.5±0.22a , 12.0±0.18c and 16.0±0.19b mm), and E. faecalis (18.75±0.23a , 11.50±0.17b and 11.5±0.12b mm) respectively. In conclusion, B. subtilis OPG3 used in this study was able to reduce silver nitrate for the biosynthesis of silver nanoparticles which can be harnessed for the treatment of pathogenic bacteria.
Keywords: silver nanoparticles, Bacillus subtilis, nanoparticles characterization, biogenic synthesis, antibacterial agent.