Antibacterial Activity of Colloidal Silver against Gram-Negative and Gram-Positive Bacteria

Abstract

Due to the emergence of antimicrobial resistance, new alternative therapies are needed. Silver was used to treat bacterial infections since antiquity due to its known antimicrobial properties. Here, we aimed to evaluate the in vitro activity of colloidal silver (CS) against multidrug-resistant (MDR) Gram-negative and Gram-positive bacteria. A total of 270 strains (Acinetobacter baumannii (n = 45), Pseudomonas aeruginosa (n = 25), Escherichia coli (n = 79), Klebsiella pneumoniae (n = 58)], Staphylococcus aureus (n = 34), Staphylococcus epidermidis (n = 14), and Enterococcus species (n = 15)) were used. The minimal inhibitory concentration (MIC) of CS was determined for all strains by using microdilution assay, and time–kill curve assays of representative reference and MDR strains of these bacteria were performed. Membrane permeation and bacterial reactive oxygen species (ROS) production were determined in presence of CS. CS MIC90 was 4–8 mg/L for all strains. CS was bactericidal, during 24 h, at 1× and 2× MIC against Gram-negative bacteria, and at 2× MIC against Gram-positive bacteria, and it did not affect their membrane permeabilization. Furthermore, we found that CS significantly increased the ROS production in Gram-negative with respect to Gram-positive bacteria at 24 h of incubation. Altogether, these results suggest that CS could be an effective treatment for infections caused by MDR Gram-negative and Gram-positive bacteria.

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.…”

Cu(i) diimine complexes as immobilised antibacterial photosensitisers operating in water under visible light

“…More accessible alternatives are therefore beginning to be developed as photosensitisers. [24][25][26][27][28][29][30] Metal ions such as Ag + , 31,32 metal oxides such as ZnO, 33 and complexes based on various metal ions including Cu(I), 34 have shown to be toxic to bacteria without light; 31,32,34 whilst inherently phototoxic metal nanoparticles have been used together with photosensitisers to promote the photoactivated production of ROS to initiate bacterial killing. 33,35 Other well-known photosensitisers include porphyrins, 36,37 such as derivatives of Zn(II) porphyrazine, or 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin tetra-iodide (tetra-Py + -Me), which have also been used for water treatment with good results: for example, tetra-Py + -Me at 10 mM achieved a reduction of 99.999% of E. coli after 120 min of irradiation with artificial white light (380-700 nm).…”

Current Perspective on Nasal Delivery Systems for Chronic Rhinosinusitis

“…Because of the emergence of antibiotic resistance, new alternative therapies are needed. Colloidal silver (CS) shows anti-biofilm properties in multidrug-resistant bacteria [ 61 ]. The suspension of submicroscopic silver particles does not directly attack bacteria but leads to the inactivation of enzymes responsible for bacterial respiration, reproduction, and metabolism by forming homo-base pairs with guanine, targeting sulfhydryl group to form S-silver bonds, and mediating membrane alteration [ 62 ].…”