1 Antimicrobial potential of bioactive metabolites, Silver nanoparticle from Bacillus spp. 2 and some antibiotics against Multidrug Resistant Salmonella spp. 3 4 Bukola Christianah Adebayo-Tayo, Oluwadara Ekundayo-Obaba and Olutayo Israel 5 Falodun 6 7 Department of Microbiology, University of Ibadan, Ibadan, Oyo State, Nigeria. 8 Email: bukola.tayo@gmail.com 9 Telephone +234 8035522409 10 Running Title: Antagonistic potential of metabolite and nanoparticles from Bacillus sp. 30 ABSTRACT 31 Objective: The synthesis of nanoparticles using microorganism and their metabolites 32 are of increasing interest because they are potential producer of biocompatible and 33 environmental friendly nanoparticles. Their nanoparticles can serve as potent 34 alternatives to antibiotics against multidrug resistance bacteria (MDR). Antibacterial 35 potential of Bacillus spp. metabolite, its silver nanoparticles and some antibiotics against 36 multi drug resistant Salmonella spp. was evaluated. 37 Method: The antimicrobial potential of metabolites from Bacillus spp. was determined 38 and SNPs biosynthesized using the metabolites was characterized. The effect of 39 physicochemical parameters on SNPs biosynthesis, antimicrobial activity of the SNPs 40 and combination of SNPs and antibiotics against Multidrug Resistant (MDR) Salmonella 41 strains were evaluated. 42 Result: The bioactive metabolites of the Bacillus spp. exhibited varied antimicrobial 43 potential against the tested MDR Salmonella spp. The metabolites were able to bio- 44 reduced AgNO3 to Ag 0 for SNPs biosynthesis. Change in colour from whitish to darkish 45 brown and Surface Plasma Resonance (SPR) peak of 600 – 800 nm was observed. 46 The SNPs were aggregated, rods and crystalline in shape and the sizes were 15 µm, 16 47 µm and 13 µm. Carboxylic acid, amino acid, alcohol, esters and aldehydes were the 48 functional group found in the biosynthesized SNPs. The antibacterial activity of BAC1- 49 SNPs, BAC7-SNPs and BAC20-SNPs against the MDRSA9 and MDRSA18 ranged uncorrected proof