In this study, Lactic Acid Bacteria isolated from traditional fermented foods were screened for the synthesis of silver nanoparticles. Antimicrobial activity of the synthesized nanoparticles was assayed against several multi-drug resistant clinical human pathogenic bacteria. Among the bacterial isolates that were tested, K1.16 and MM17 had 99% and 98% relatedness with Lactobacillus herbarum strain TCF032 E4 and Lactobacillus paraplantarum strain DSM 10667 respectively, and were able to reduce silver efficiently into silver nanoparticles. The Ultraviolet–Visible spectrum showed a plasmon peak at ~ 410 nm confirming the presence of silver nanoparticles. Energy dispersive X-ray spectrum revealed a strong signal in the silver region confirming the formation of silver nanoparticles as well as a optical absorption peak at approximately 3 KeV due to surface plasmon resonance. Diffraction peaks were observed at 38.1°, 44.2°, 64.4° and 77.4° in the 2θ range. The peaks were indexed to (111), (200), (220) and (311) which can be indexed according to the facets of a face centered cubic crystal structure of silver. Scanning transmission electron microscope micrographs recorded from the coated grid of the synthesized nanoparticles showed a spherical shape of silver nanoparticles with the size range of 11-71 nm. Silver nanoparticles produced by Lactobacillus plantarum (K1.16) were the most potent as indicated by the lowest minimum inhibitory concentrations across all pathogenic bacterial isolates tested in this study, which included; Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Salmonella Typhimurium, Bacillus cereus and Enterobacter spp. These findings can be pertinent in the development of novel topical ointments against pathogenic microorganisms.

Keywords: Lactic acid bacteria (LAB), silver nanoparticles (AgNPs), antimicrobial, Energy dispersive x-ray (EDX), Scanning transmission electron microscope (STEM).

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