Biogenic Synthesis of Chitosan/Silver Nanocomposite by Escherichia coli D8 (MF062579) and its Antibacterial Activity

Abstract

Silver nanomaterials are usually applied as antimicrobial agents; however, they can cause toxic effects on human health. The current investigation was performed to study the combined effects of chitosan and silver nanoparticles (AgNPs) using the cell-free supernatant of Escherichia coli (MF062579). The produced chitosan/silver nanocomposite (CS/AgNC) showed good antibacterial activity and high stability. The biosynthesized CS/AgNC contained homogeneous spherical AgNPs with an average size of ~12.3 nm and a net surface charge of +30.9 ± 3.2 mV. CS/AgNC revealed a good minimum inhibitory concentration (MIC) result against Gram-negative (G-ve, E. coli) and Gram-positive (G+ve, Bacillus cereus) bacteria with inhibition ratios of 80.7% and 75.5%, respectively. Nanocomposite-treated cells displayed complete lysis of the bacterial cell, a low amount of DNA, and cell membrane and wall disruption. Glutamate dehydrogenase (GDH) and malate dehydrogenase (MDH) activities of tested bacterial strains were demonstrated using spectrophotometry and electrophoresis on a non-denaturing acrylamide gel. In CS/AgNC-treated strains, enzyme production and activity were fewer than in untreated strains. The obtained results suggested that CS/AgNC seems to be more effective against G-ve than G+ve bacteria.