Biosynthesis of silver nanoparticles with potent antimicrobial activity using lactic acid bacteria

Abstract

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.