Interaction of silver nanoparticles with Escherichia coli and their cell envelope biomolecules

Abstract

The antibacterial effect of AgNPs was investigated by determining MIC/MBC and growth kinetics assay. The lowest MIC/MBC was found to be in the range of 11.25-22.5 µg ml(-1) . The growth kinetics curve shows that 25 µg ml(-1) AgNPs strongly inhibits the bacterial growth. Confocal laser scanning electron microscopy (CLSM) shows that as the concentration of NPs increases, reduction in the number of cells was observed and at 50 µg ml(-1) of NPs, 100% death was noticed. Scanning electron microscopy (SEM) shows cells were severely damaged with pits, multiple depressions, and indentation on cell surface and original rod shape has swollen into bigger size. High resolution-transmission electron microscopic (HR-TEM) micrograph shows that cells were severely ruptured. The damaged cells showed either localized or complete separation of the cell membrane. The NPs that anchor onto cell surface and penetrating the cells may cause membrane damage, which could result in cell lysis. The interaction of AgNPs to membrane biomolecules; lipopolysaccharide (LPS) and L-α-phosphatidyl-ethanolamine (PE) were investigated by attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy. LPS and PE showed IR spectral changes after AgNPs exposure. The O-antigen part of LPS was responsible for interaction of NPs through hydrogen bonding. The phosphodiester bond of PE was broken by AgNPs, forming phosphate monoesters and resulting in the highly disordered alkyl chain. The AgNPs-induced structural changes in phospholipid may lead to the loss of amphiphilic properties, destruction of the membrane and cell leaking. The biomolecular changes in bacterial cell envelope revealed by ATR-FTIR provide a deeper understanding of cytotoxicity of AgNPs.

Nanomaterials for alternative antibacterial therapy

“…[28][29][30] On the other hand, upsurge in resistance to Ag NPs has been reported due to genetic alterations in bacteria. 31 The deposition of silver 32 The high toxicity of CuO NPs causes oxidative lesions, while DNA damage induced by ZnO and TiO 2 NPs limits the efficacy of these NPs. Nonetheless, NPs have emerged as alternative antimicrobial approach to combat biofilms and for treating severe bacterial infections.…”

“…38 Al 2 O 3 NPs cause oxidative damage to membrane and enter cytoplasm. 32 Ag and Au NPs have been reported to exert toxicity by penetrating inside the cell and denaturing 30S ribosomal subunit, thereby impeding protein translation.…”

Antimicrobial Performance of Thermoplastic Elastomers Containing Zinc Pyrithione and Silver Nanoparticles

“…One of the mechanisms of silver ion release from polymeric matrix occurs through contact of metallic silver with dissolved oxygen in moisture 15,16 . Once released, AgNano will act on the microbial cells through several modes of action 17 , such as: (a) nanoparticles can bind to proteins of vital enzymes presents in the mycelial 18 and bacterial 19 cell wall, (b) also can damage the cellular structures and biomolecules 20 , (c) cause toxicity by the generation of reactive oxygen species 21 , besides (d) affecting in the molecular and cellular routes of bacteria. Recently, silver nanoparticles have been pointed out as the most innovative and efficient antibacterial form 16 , since they provide better dispersion in the polymeric matrix 22 .…”

The antimicrobial activity of nanoparticles: present situation and prospects for the future

“…Structural changes in the phospholipid lead to the loss of parent molecules, destruction of the cell membrane, and cytoplasmic leakage. 119 One of the foremost functions of the cell membrane is in the respiratory activity of bacteria. Studies have reported that NPs disrupt the respiratory activity of the bacterial cell membrane, which can be analyzed by detecting the uptake of O 2 or the reduction in 2,3,5-triphenyltetrazolium chloride (TTC).…”