Ag/SiO2 nanocomposite mediated by Escherichia coli D8 and their antimicrobial potential

Silica (SiO2) has a fundamental role in the recuperation of plants in response to environmental stresses, besides the induction of resistance against plant diseases. Silver nanoparticles (AgNPs) have a superior antimicrobial activity. The combination between SiO2 and AgNPs is a promising approach due to their antimicrobial activity, biological activity, low toxicity, and high stability of the produced nanocomposite. The current study postulated a green method for silver/silica nanocomposite (Ag/SiO2NC) synthesis at room temperature using the crude metabolites of Escherichia coli D8 (MF062579) strain in the presence of sunlight. UV-Vis spectrophotometry, X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) analyses have characterized the biosynthesized nanocomposite. TEM study of Ag/SiO2NC showed an average particle size of ~32 – 48 nm whereas AgNPs showed a mean size of 18 – 24 nm. The negative charged Ag/SiO2NC (-31.0 mV) showed potent antimicrobial activity against Bacillus cereus ATCC6633, Klebsiella pneumoniae ATCC33495, Staphylococcus aureus (ATCC25923), E. coli (ATCC25922), Candida albicans (ATCC10231), and Botrytis cinerea (Pers: Fr.). The minimum inhibitory concentration (MIC) test showed a dose-dependent manner of Ag/SiO2NC antimicrobial action. MIC values of Ag/SiO2NC against the tested pathogens exhibited 125 and 6.25 μg.mL-1 as antibacterial and antifungal agents, respectively. TEM micrographs showed changes in the pathogens treated with Ag/SiO2NC including wrinkling, damage, and rupture of the bacterial cell membrane. In addition, the formation of a mucilage matrix connecting the hyphal cells, the appearance of big vacuoles and lipid droplets with severe leakage of cytoplasmic contents of the treated B. cinerea were also recorded.