Antimicrobial Resistance Lab Report
Mechanisms of Silver Nanoparticle Action in Bacteria and Potential for Bacterial Resistance
The antimicrobial activity of silver in general, and of silver nanoparticles in particular, is of significant interest because it appears to be independent of the strain of bacteria. Crucially, antibiotic resistant strains, MRSA (methicillin, or multiple-resistant Staphylococcus aureus), E. coli O157, and others are affected by silver [6]. The reasons for this are not fully clear as yet, but could be related to mechanisms of silver ion action on bacteria [110], trypanosomes and yeasts, all of which can take up and concentrate silver (and copper) from dilute solutions in sufficient amounts to lead to lead to saturation of all enzyme-protein molecules per cell [6]. Other effects observed include structural changes in bacterial cell walls and intracellular and nuclear membranes as well as bacterial DNA and RNA denaturation, inhibiting replication [6,110,111]. Possibly these effects in bacterial RNA and DNA are related to (or in addition to) the observed effects on mitochondrial respiration and cytosolic protein that lead to bacterial cell death. The distinct activity of silver ions, rather than nanoparticle derived impacts, has not been understood as yet. Ovington [111] noted that nanocrystalline silver products (Acticoat®, Smith and Nephew) can …show more content…
release a cluster of highly reactive silver cations and radicals, which provide a high antibacterial potency.
Li et al. [29] point out three possible antibacterial mechanisms of silver nanoparticles:
(1) Adhesion of nanoparticles to the bacteria surface, altering the membrane properties.
The small size and extremely large surface area of nanoparticles enables them to make strong contact with the microorganism surface [5]. As stated by Cao et al. [31] who studied the antibacterial properties of silver nanoparticles embedded in titanium (Ag-PIII-originated surface), the attachment of bacteria to such a surface correlates with the surface zeta potential of the nanoparticles. All studied Ag-PIII surfaces reduced the proliferation of both types of bacteria studied (Gram-positive Staphylococcus aureus and Gram-negative Escherichia
coli).
(2) Silver nanoparticles penetrating inside the bacterial cell, resulting in DNA damage. In the study of Choi and Hu [59] the inhibition of nitrifying organisms was correlated with the fraction of silver nanoparticles less than 5 nm, which was more toxic than any other form of silver (silver ions, AgCl colloids). The authors suggest that this may be due to easier (active) transport through the cell membrane of uncharged silver nanoparticles than of charged silver ions.
The antimicrobial activity of silver in general, and of silver nanoparticles in particular, is of significant interest because it appears to be independent of the strain of bacteria. Crucially, antibiotic resistant strains, MRSA (methicillin, or multiple-resistant Staphylococcus aureus), E. coli O157, and others are affected by silver [6]. The reasons for this are not fully clear as yet, but could be related to mechanisms of silver ion action on bacteria [110], trypanosomes and yeasts, all of which can take up and concentrate silver (and copper) from dilute solutions in sufficient amounts to lead to lead to saturation of all enzyme-protein molecules per cell [6]. Other effects observed include structural changes in bacterial cell walls and intracellular and nuclear membranes as well as bacterial DNA and RNA denaturation, inhibiting replication [6,110,111]. Possibly these effects in bacterial RNA and DNA are related to (or in addition to) the observed effects on mitochondrial respiration and cytosolic protein that lead to bacterial cell death. The distinct activity of silver ions, rather than nanoparticle derived impacts, has not been understood as yet. Ovington [111] noted that nanocrystalline silver products (Acticoat®, Smith and Nephew) can …show more content…
release a cluster of highly reactive silver cations and radicals, which provide a high antibacterial potency.
Li et al. [29] point out three possible antibacterial mechanisms of silver nanoparticles:
(1) Adhesion of nanoparticles to the bacteria surface, altering the membrane properties.
The small size and extremely large surface area of nanoparticles enables them to make strong contact with the microorganism surface [5]. As stated by Cao et al. [31] who studied the antibacterial properties of silver nanoparticles embedded in titanium (Ag-PIII-originated surface), the attachment of bacteria to such a surface correlates with the surface zeta potential of the nanoparticles. All studied Ag-PIII surfaces reduced the proliferation of both types of bacteria studied (Gram-positive Staphylococcus aureus and Gram-negative Escherichia
coli).
(2) Silver nanoparticles penetrating inside the bacterial cell, resulting in DNA damage. In the study of Choi and Hu [59] the inhibition of nitrifying organisms was correlated with the fraction of silver nanoparticles less than 5 nm, which was more toxic than any other form of silver (silver ions, AgCl colloids). The authors suggest that this may be due to easier (active) transport through the cell membrane of uncharged silver nanoparticles than of charged silver ions.