Natural flagella-templated Au nanowires as a novel adjuvant against Listeria monocytogenes

Authors: DU, RENJI - Northeast Forestry University; QU, YUEJUN - Northeast Forestry University; Qi, Phoebe; SUN, XINGBIN - Northeast Forestry University; Liu, Yanhong; ZHAO, MIN - Northeast Forestry University

Submitted to: The Royal Society of Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2020
Publication Date: 2/26/2020
Citation: Du, R., Qu, Y., Qi, P.X., Sun, X., Liu, Y., Zhao, M. 2020. Natural flagella-templated Au nanowires as a novel adjuvant against Listeria monocytogenes. The Royal Society of Chemistry. Nanoscale. 12:5627-5635.
DOI: https://doi.org/10.1039/c9nr10095d

Interpretive Summary: A nanowire is a very long and thin wire made of stable heavy metals with a diameter in the order of nanometers (nm) or less. A nanowire can be used as a catalyst to speed up or slow down a chemical reaction. Plant extracts such as olive leaf extract can be used to kill bacterial pathogens such as Listeria monocytogenes; however, large amounts of extract are needed to inhibit the growth of pathogens. To enhance killing of pathogens with extract, a nanowire was synthesized using bacterial flagella (a long thin structure on the surface of bacteria) as the substrate. Application of the synthesized nanowires reduced the amount of plant extracts needed to inhibit the growth of L. monocytogenes. In addition, nanowires are safe to use and have the potential to be employed in food packaging materials to enhance food safety.

Technical Abstract: A simple method was developed for the extraction and purification of bacterial flagella with a yield of a concentration of 113.22 ± 5.64 mg/mL. Gold (Au) nanowires were synthesized using the bacterial flagella as the template. Transmission Electron Microscopy (TEM) analysis showed that the nanowires were scarcely clustered as stiff (no tendency to bend or fold) and straight nanorods with homogeneous surface and a uniform aspect ratio over 60. Fourier Transform Infrared (FT-IR) spectroscopic studies revealed the deep involvement of the functional groups located within and on the surface of flagellin, including C-N, N-H, O-H, and C=O. The profound transformation observed in the absorption profiles of these groups supported the notion that both chemical (reduction) reaction and physical (electrostatic) binding of Au occurred during the formation of Au nanowires. Verbascoside, oleuropein, and olive leaf extract (OLE) have been shown to inhibit the growth of Listeria monocytogenes completely at their respective Minimal Inhibitory Concentrations (MICs) of 20, 64, and 64 mg/mL. In contrast, the synthesized Au nanowires demonstrated high electrocatalytic activity and reduced the MICs of the three antibacterial compounds by half. Moreover, results from the AMES assays indicated that the synthesized Au nanowires had no mutagenic activities at the catalytic concentration used, 128 ug/mL. Therefore, the Au nanowires fabricated in this work have the potential to be used as new antimicrobial food packaging materials to enhance food safety.