Effects of sublethal concentrations of silver nanoparticles on Escherichia coli and Bacillus subtilis under aerobic and anaerobic conditions (original) (raw)
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PLOS ONE, 2015
The superior antimicrobial properties of silver nanoparticles (Ag NPs) are well-documented, but the exact mechanisms underlying Ag-NP microbial toxicity remain the subject of intense debate. Here, we show that Ag-NP concentrations as low as 10 ppm exert significant toxicity against Bacillus subtilis, a beneficial bacterium ubiquitous in the soil. Growth arrest and chromosomal DNA degradation were observed, and flow cytometric quantification of propidium iodide (PI) staining also revealed that Ag-NP concentrations of 25 ppm and above increased membrane permeability. RedoxSensor content analysis and P hag-GFP expression analysis further indicated that reductase activity and cytosolic protein expression decreased in B. subtilis cells treated with 10-50 ppm of Ag NPs. We conducted X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses to directly clarify the valence and fine structure of Ag atoms in B. subtilis cells placed in contact with Ag NPs. The results confirmed the Ag species in Ag NP-treated B. subtilis cells as Ag 2 O, indicating that Ag-NP toxicity is likely mediated by released Ag + ions from Ag NPs, which penetrate bacterial cells and are subsequently oxidized intracellularly to Ag 2 O. These findings provide conclusive evidence for the role of Ag + ions in Ag-NP microbial toxicity, and suggest that the impact of inappropriately disposed Ag NPs to soil and water ecosystems may warrant further investigation.
Culture Method-Dependent Variation in the Sensitivity of Escherichia coli to Silver Nanoparticles
Advances in Materials Science and Engineering
Preparation of various metal nanoparticles using plant extracts has been well studied in recent years. In this study, we found that nanoparticles synthesized using the extracts of the inflorescence of Cocos nucifera exhibited differential inhibitory activity against Escherichia coli depending on the nature of the bacterial culture source. Incorporation of silver nanoparticles (Ag-NPs) into the nutrient broth culture of E. coli resulted in poor inhibitory activity. However, when the silver nanoparticles are added to nutrient agar plates used for culture of E. coli, effective inhibition was observed. Additionally, E. coli in broth culture resisted the inhibitory effects of Ag-NPs by forming aggregates of bacterial cells. The aggregates then generated a protective zone around the colonies to prevent the entry of Ag-NPs, and the bacterial cells multiplied without inhibition by the Ag-NPs. These differential effects of Ag-NPs on E. coli culture grown in nutrient broth and on nutrient aga...
BioMetals, 2012
In this study, the conditions and mechanism of antibacterial activity of hydrophilic polymer coated silver nanoparticles (AgNPs) against E. coli O157:H7 (CMCC44828) as model pathogen was studied. The AgNPs were coated with amphiphilic polymer that introduced carboxyl groups on the surface to make it water-soluble. The AgNPs were exposed to various treatment conditions of pH and temperature before these were combined with the E. coli. The mechanism of the antibacterial activity was studied through the formation of reactive oxygen species (ROS) that was later suppressed with antioxidant to establish correlation with the AgNPs antimicrobial activity. Studies were carried out at both anaerobic and aerobic conditions. The results indicated that 5 mg/L AgNPs inhibited *50% of the growth of 10 6 colony forming units per milliliter (cfu/mL) E. coli cells in liquid Luria-Bertani (LB) medium. This dose-dependent antimicrobial activity was higher at increased temperature (37°C) but was lower when the AgNPs were treated with acid at pH 2 before exposure to the bacteria. It was also established that the conditions of higher antimicrobial effect generated more ROS that was dependent on the presence of oxygen. The antibacterial activity was suppressed in the presence of an antioxidant.
Antibacterial activity and mechanism of silver nanoparticles on Escherichia coli
Applied microbiology …, 2010
The antibacterial activity and acting mechanism of silver nanoparticles (SNPs) on Escherichia coli ATCC 8739 were investigated in this study by analyzing the growth, permeability, and morphology of the bacterial cells following treatment with SNPs. The experimental results indicated 10 μg/ml SNPs could completely inhibit the growth of 10 7 cfu/ml E. coli cells in liquid Mueller-Hinton medium. Meanwhile, SNPs resulted in the leakage of reducing sugars and proteins and induced the respiratory chain dehydrogenases into inactive state, suggesting that SNPs were able to destroy the permeability of the bacterial membranes. When the cells of E. coli were exposed to 50 μg/ml SNPs, many pits and gaps were observed in bacterial cells by transmission electron microscopy and scanning electron microscopy, and the cell membrane was fragmentary, indicating the bacterial cells were damaged severely. After being exposed to 10 μg/ml SNPs, the membrane vesicles were dissolved and dispersed, and their membrane components became disorganized and scattered from their original ordered and close arrangement based on TEM observation. In conclusion, the combined results suggested that SNPs may damage the structure of bacterial cell membrane and depress the activity of some membranous enzymes, which cause E. coli bacteria to die eventually.
Journal of Hazardous Materials, 2011
This study explores the potential antimicrobial mechanisms of commercial silver nanoparticles (Ag NPs) in the environmental bacterium, Pseudomonas chlororaphis O6. The 10 nm size NPs aggregated in water, as demonstrated by atomic force microscopy. Solubility of the NPs at 10 mg/L was 0.28 mg/L (pH 6) and 2.3 mg/L (pH 7); release from 10 mg/L bulk Ag was below detection. The NPs eliminated cell culturability at 3 mg/L, whereas no effect was observed at 10 mg/L bulk Ag. Zeta potential measurements revealed that the NPs were negatively charged; unlike Ag ions, their addition to the negatively charged cells did not change cell charge at pH 6, but showed a trend to reduce cell charge at pH 7. Isolated extracellular polymeric substances (EPS) from PcO6 was polydisperse, with negative charge that was neutralized by Ag ions, but not by the NPs. Addition of EPS eliminated Ag NP's toxicity in cells lacking EPS. Intracellular accumulation of • OH was not detected in NP-treated cells; however, the use of scavengers suggested the NPs caused extracellular H 2 O 2 production. No evidence was found for loss of membrane integrity upon treatment with the NPs. Our findings indicate that growth of environmental bacteria could be impaired by Ag NPs, depending on the extent of EPS production.
Antibacterial Effects of Silver Nanoparticles on Escherichia coli and Bacillus subtilis
Metal nanoparticles have been intensively studied within the past decade. Nanosized materials have been an important topic in basic and applied sciences. In this work we synthesized silver nanoparticles by Salmonella typhirium. The silver nanoparticles displayed characteristic Surface Plasmon Resonance peak at around 422 nm. In addition, the morphology of nanoparticles was observed by transmission electron microscopy. The size of the nanoparticles was determined to be 65 nm, applying dynamic light scattering. The main objective of this work is the study of antibacterial effects of silver nanoparticles. Silver nanoparticles showed high antibacterial activity against Escherichia coli and Bacillus subtilis bacteria.
Biochemical and Biophysical Research Communications, 2012
Despite extensive use of silver nanoparticles for antimicrobial applications, cellular mechanisms underlying microbial response to silver nanoparticles remain to be further elucidated at the systems level. Here, we report systems-level response of Escherichia coli to silver nanoparticles using transcriptomebased biochemical and phenotype assays. Notably, we provided the evidence that anaerobic respiration is induced upon exposure to silver nanoparticles. Further we showed that anaerobic respiration-related regulators and enzymes play an important role in E. coli resistance to silver nanoparticles. In particular, our results suggest that arcA is essential for resistance against silver NPs and the deletion of fnr, fdnH and narH significantly increases the resistance. We envision that this study offers novel insights into modes of antimicrobial action of silver nanoparticles, and cellular mechanisms contributing to the development of microbial resistance to silver nanoparticles.
Interaction of silver nanoparticles with Escherichia coli and their cell envelope biomolecules
Journal of Basic Microbiology, 2013
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...