Enhancement of the Antibacterial Efficiency of Silver Nanoparticles against Gram-Positive and Gram-Negative Bacteria Using Blue Laser Light

Abstract

Silver nanoparticles (Ag-NPs) possess excellent antibacterial properties and are considered to be an alternative material for treating antibiotic-resistant bacteria. The present study was aimed at enhancing the antibacterial efficiency of Ag-NPs using visible laser light against Escherichia coli and Staphylococcus aureus in vitro. Four concentrations of Ag-NPs (12.5, 25, 50, and 100 μg/ml), synthesized by the chemical reduction method, were utilized to conduct the antibacterial activity of prepared Ag-NPs. The antibacterial efficiencies of photoactivated Ag-NPs against both bacteria were determined by survival assay after exposure to laser irradiation. The mechanism of interactions between Ag-NPs and the bacterial cell membranes was then evaluated via scanning electron microscopy (SEM) and reactive oxygen species analysis to study the cytotoxic action of photoactivated Ag-NPs against both bacterial species. Results showed that the laser-activated Ag-NP treatment reduced the surviving population to 14% of the control in the E. coli population, while the survival in the S. aureus population was reduced to 28% of the control upon 10 min exposure time at the concentration of 50 μg/ml. However, S. aureus showed lower sensitivity after photoactivation compared to E. coli. Moreover, the effects depended on the concentration of Ag-NPs and exposure time to laser light. SEM images of treated bacterial cells indicated that substantial morphological changes occurred in cell membranes after treatment. The results suggested that Ag-NPs in the presence of visible light exhibit strong antibacterial activity which could be used to inactivate harmful and pathogenic microorganisms.

In vitro biological activity of Hydroclathrus clathratus and its use as an extracellular bioreductant for silver nanoparticle formation

“…Studies have shown that Gram-positive bacteria are more susceptible to AgNPs, compared to Gramnegative bacteria due to their structural differences. Contradicting earlier findings [38,39], we found no biased antibacterial action against either Gram-positive or Gramnegative bacteria, which could be attributed to the charge difference between the AgNPs and bacterial cells [32].…”

Probing the Mode of Antibacterial Action of Silver Nanoparticles Synthesized by Laser Ablation in Water: What Fluorescence and AFM Data Tell Us

“…The intensity of the fluorescence signal is proportional to the amount of ROS [ 28 ]. The research data obtained from previous reports suggest that: treatment with AgNPs alone did not induce significant ROS formation [ 29 ]; a significant increase in the DCF fluorescence intensity was observed for AgNP-treated bacterial cells [ 30 ]; colloidal silver significantly increased the production of ROS when compared with untreated cells [ 31 ]; ROS played a very important role in the antibacterial mechanism of AgNPs [ 32 ]. Interestingly, ROS detection data in AgNP-treated E. coli [ 33 ] showed that the fluorescence signal of AgNP-treated cells is lower than for the non-treated cells, for most treatment concentrations.…”

<p>Silver Nanoparticles for the Therapy of Tuberculosis</p>

“…As in the case of the Gram-positive bacteria, this structural particularity prevents the action of Ag-NPs rendering acid-fast and gram-positive bacteria more resistance to the antimicrobial activity of Ag-NPs comparatively with Gram-positive bacteria. 143,144 For example, the Grampositive Bacillus subtilis, have a cell wall of 55.4 nm, the acid-fast M tuberculosis a 20.2 nm 145 while the Gramnegative Pseudomonas aeruginosa, has a cell wall of only a 2.4 nm. 146 Interestingly, although there are important functional differences between the mycobacteria cell wall and gram-positive bacteria, the DNA-based molecular taxonomy of bacteria based on the high similarity to genes, groups the classical acid fast-mycobacteria as gram-positive bacteria.…”

“…Additionally to the wall thickness and structure, the difference in resistance of different classes of bacteria can be explained by the fact that due to the high-presence of LPS the cell wall, Gram-negative bacteria has a higher negative charge, which promotes local adhesion and membraneclustering of particles and finally enhances the antibacterial effect of Ag-NPs. 144,162,163 Therefore, electrostatic interaction between bacterial cells (charged negatively) and AgNPs (charged positively) is critical for the antibacterial activity of NPs. 144,161,164 Moreover, to the above-mentioned action against the bacterial wall, AgNPs have the ability to enter inside bacteria's cytosol, to form cytoplasmic precipitates and to disrupt several bacterial-physiological processes.…”

“…144,162,163 Therefore, electrostatic interaction between bacterial cells (charged negatively) and AgNPs (charged positively) is critical for the antibacterial activity of NPs. 144,161,164 Moreover, to the above-mentioned action against the bacterial wall, AgNPs have the ability to enter inside bacteria's cytosol, to form cytoplasmic precipitates and to disrupt several bacterial-physiological processes. The type of bacterial-metabolic pathways disrupted directly by the Ag in particle state is largely unknown.…”