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Review
. 2016 Nov 16;7:1831.
doi: 10.3389/fmicb.2016.01831. eCollection 2016.

Mechanistic Basis of Antimicrobial Actions of Silver Nanoparticles

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Free PMC article
Review

Mechanistic Basis of Antimicrobial Actions of Silver Nanoparticles

Tikam Chand Dakal et al. Front Microbiol. .
Free PMC article

Abstract

Multidrug resistance of the pathogenic microorganisms to the antimicrobial drugs has become a major impediment toward successful diagnosis and management of infectious diseases. Recent advancements in nanotechnology-based medicines have opened new horizons for combating multidrug resistance in microorganisms. In particular, the use of silver nanoparticles (AgNPs) as a potent antibacterial agent has received much attention. The most critical physico-chemical parameters that affect the antimicrobial potential of AgNPs include size, shape, surface charge, concentration and colloidal state. AgNPs exhibits their antimicrobial potential through multifaceted mechanisms. AgNPs adhesion to microbial cells, penetration inside the cells, ROS and free radical generation, and modulation of microbial signal transduction pathways have been recognized as the most prominent modes of antimicrobial action. On the other side, AgNPs exposure to human cells induces cytotoxicity, genotoxicity, and inflammatory response in human cells in a cell-type dependent manner. This has raised concerns regarding use of AgNPs in therapeutics and drug delivery. We have summarized the emerging endeavors that address current challenges in relation to safe use of AgNPs in therapeutics and drug delivery platforms. Based on research done so far, we believe that AgNPs can be engineered so as to increase their efficacy, stability, specificity, biosafety and biocompatibility. In this regard, three perspectives research directions have been suggested that include (1) synthesizing AgNPs with controlled physico-chemical properties, (2) examining microbial development of resistance toward AgNPs, and (3) ascertaining the susceptibility of cytoxicity, genotoxicity, and inflammatory response to human cells upon AgNPs exposure.

Keywords: antimicrobial activity; cytotoxicity; genotoxicity; inflammatory response; multidrug resistance; physico-chemical property; silver nanoparticles.

Figures

Figure 1
Figure 1
Schematic representation of synthesis of colloidal silver nanoparticles using chemical reduction process. Silver ions (Ag+) subjected to chemical reduction to form silver atoms (Ag0). These atoms undergo nucleation to form primary AgNPs that further coalesce with each other to form final AgNPs.
Figure 2
Figure 2
The four most prominent routes of antimicrobial action of AgNPs. 1, AgNPs adhere to microbial cell surface and results in membrane damage and altered transport activity; 2, AgNPs penetrate inside the microbial cells and interact with cellular organelles and biomolecules, and thereby, affect respective cellular machinery; 3, AgNPs cause increase in ROS inside the microbial cells leading to cell damage and; 4, AgNPs modulate cellular signal system ultimately causing cell death.
Figure 3
Figure 3
AgNPs exposure to human or mammalian cells. AgNPs induce cytotoxic, genotoxic and inflammatory response in human and mammalian cells and consequently trigger apoptotic cell death, carcinogenesis and fibrosis.

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