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Mechanisms of nanoparticle antimicrobial action

Nanoparticles as antimicrobials Recent research has been focused on antimicrobial nanoparticles composed of metals, e.g., platinum or silver; metal oxides such as TiO2 and CuO; hydroxides such as Mg(OH)2, as well as some from biodegradable materials, including dextran and chitosan (Figure 1).

The present understanding of the possible mechanisms by which nanoparticles of different materials kill microbial cells is still patchy and incomplete. Although various mechanisms of their antimicrobial activity have been explored, most of the research in this area is still ongoing. Some of the mechanisms of particle attachment to the microbial cells and pathways of cell damage are illustrated in Figure 2.

Different methods for assessment of their antimicrobial action have been used, e.g., estimation of the MIC, growth inhibition method and minimum bactericidal concentration. The antimicrobial activity is tested on specific groups of pathogens such as E. coli, Pseudomonas aeruginosa, Staphylococcus aureus, etc. Silver

crobial drug iers

Gold Dextran/ PGLA cores

Titanium dioxide

Metals

Metal oxides

Types of nanoparticles

Copper oxide

Metal hydroxides

Zinc oxide Dentistry

Biodegradable and hybrid nanoparticles

Magnetite + PGA

Magnetite + Chitosan

und sing erials Magnesium hydroxide

Figure 1. (above) Classification of synthetic nanoparticles with antimicrobial action Deposition of silica shell

bial

1) Shell fragmentation Microbial cell 2) Bleaching of cells

Deposition of Zinc oxide NPs

Silver nanoparticles release silver ions (Ag+) which can damage the target cells through several different pathways, e.g., binding to DNA and RNA which result in their inactivation. In addition, they can also react with sulfur-containing peptides inside the cells and on the cell membrane which in turn affects their viability. It has been suggested that they can potentially destabilize cell membrane proteins and inhibit various intracellular enzymes. At high nanoparticle concentration the released silver ions affect the cytoplasm components and nucleic acids, whereas at lower concentrations they tend to inhibit respiratory chain enzymes and impair membrane permeability to protons and phosphates. Recently, gold nanoparticles have been combined with various photosensitizers which make them antimicrobial for use in photodynamic therapy. Figure 2. (below) Mechanisms of action of some antimicrobial nanoparticles

Cell membrane damage Cell wall Periplasmic space

Colloid antibodies

Cell membrane

Zn2+ Enzymes irradiation with a laser

tibodies othermal on microbial cell shape recognition

outflow of cell metabolites

Inactivation of enzymes by Ag+ or Zn2+

shape-selective killing Enzymes of microbial cells

Zn2+

Cell Death

Cosmetic ingredients

DNA / RNA damage

Ag+ ROS

Ag+

App of c

Food preservation

Inhibition of respiratory chain enzymes

Ag+

e ran mb e e lm g Cel dama

Interferes with proton and phosphate transport

Water treatment

Silver NPs

www.sfam.org.uk

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+ Ag+ Ag + Silver ion Ag Ag+

generation

Bactericidal agents

Reactive Oxygen Species

ROS

Release of bactericidal agents

Titanium dioxide NPs

UV light O2

microbiologist

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June 2014

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Profile for Society for Applied Microbiology

Microbiologist, June 2014  

Published four times a year, in March, June, September and December, this professionally produced, 60 page full-colour magazine keeps our me...

Microbiologist, June 2014  

Published four times a year, in March, June, September and December, this professionally produced, 60 page full-colour magazine keeps our me...