Multiple parameters for the comprehensive evaluation of the susceptibility of Escherichia coli to the silver ion

The susceptibility of Escherichia coli B to the antibacterial activity of silver ions was measured in terms of the initial inhibitory concentration, complete inhibitory concentration, postagent effect for bacteriostatic susceptibility, minimum bactericidal concentration, maximum tolerant concentration, and log killing time for bactericidal activity. At a concentration of 9.45 M and an inoculum size of 10 CFU ml, silver caused growth delay of E. coli; at a concentration of 18.90 M, silver completely inhibited bacterial growth. Prolonged postagent effects ranged between 1.5 and 12 h at 0.75 x the initial inhibitory concentration, 1.0 x the initial inhibitory concentration, and 1.5 x the initial inhibitory concentration of the silver ion. One log-unit of viable bacterial population size was lost every 30 min at the minimum bactericidal concentration of the silver ion. Silver tolerance was determined as 20 times the initial inhibitory concentration with 48 h of exposure. This study presents an evaluative model as a reference for the quantitative analysis of the susceptibility of bacteria to silver ions. © Rapid Science 1998.     

Syntheses, thermal analyses, crystal structures and antimicrobial properties of silver(I)-saccharinate complexes with diverse diamine ligands

Five new silver(I)-saccharinate complexes [Ag₂(sac)₂(tmen)₂] (1), [Ag₂(sac)₂(deten)₂] (2), [Ag₂(sac)₂(dmen)₂] (3), [Ag(sac)(N,N-eten)] (4), and [Ag(sac)(dmpen)]_n (5); (sac = saccharinate, tmen = N,N,N′,N′-tetramethylethylenediamine, deten = N,N′-diethylethylenediamine, dmen = N,N′-dimethylethylenediamine, N,N-eten = N,N-diethylethylenediamine and dmpen = 1,3-diamino-2,2-dimethylpropan) have been synthesized and characterized by elemental analyses, IR, thermal analyses, single crystal X-ray diffraction and antimicrobial activities. The crystallographic analyses show that all the complexes crystallize in monoclinic space group P2₁/c. In 1, the sac ligand acts as a bridge to connect the silver centres through its imino N and carbonyl O atoms forming an eight-membered bimetallic ring in a chair conformation. Complex 2 has also a dimeric structure in which the monomeric [Ag(sac)(deten)] units are linked by Ag?Ag interactions. In 3, saccharinate ligand acts as a bridging bidentate ligand between two silver(I) centres through sulfonyl group and imino N atom, forming an alternating polymeric chain through the direction [0 1 0]. In 4, the inter-molecular N-H?O hydrogen bonds form one-dimensional polymeric chains through the a axis, and these linear chains are inter-connected to each other by N-H?O hydrogen bonds, which produce a chain of edge-fused and rings along [1 0 0]. Complex 5 is a coordination polymer in which the monomeric [Ag(dmpen)(sac)]_n units are linked by Ag?Ag interactions, and the dmpen ligand acts as a bridge between the silver(I) ions, forming a two-dimensional network parallel to the (1 0 0) plane.     

Non-cytotoxic silver nanoparticle-polyvinyl alcohol hydrogels with anti-biofilm activity: designed as coatings for endotracheal tube materials

Endotracheal intubation is commonly associated with hospital-acquired infections as the intubation device acts as reservoir for bacterial colonization in the lungs. To reduce the incidence of bacterial colonization on the tubes, hydrogel coatings loaded with antimicrobial agents are gaining popularity. The aim of this study was to incorporate silver nanoparticles (AgNPs) into polyvinyl alcohol (PVA) to form stable hydrogels. Embedding AgNPs into PVA resulted in a decreased elongation at break and an increased tensile strength compared to PVA alone. The Ag release profile varied as a function of the degree of hydrolysis of PVA: the higher degree of hydrolysis demonstrated a lower release rate. Fourier infrared transform spectroscopy demonstrated that AgNPs interacted exclusively with the –OH groups of PVA. AgNP-loaded PVA was non-toxic against human normal bronchial epithelial cells while effective against the attachment of Pseudomonas aeruginosa and Staphylococcus aureus with a greater effect on P. aeruginosa.     

Synthesis, characterization and antimicrobial activity of new silver complexes with N-heterocyclic carbene ligands

Synthesis, structure, and antimicrobial studies of silver complexes of N-heterocyclic carbene (NHC) are reported. All the silver-NHC complexes (1a-f) were prepared from the benzimidazolium salts by the reactions with Ag₂O in dichloromethane as a solvent at room temperature. The new compounds characterized by ¹H NMR, ¹³ C NMR, IR and elemental analysis techniques which support the proposed structures. Chloro[1-(2,4,6-trimethylbenzyl)-3-(methoxyethyl)benzimidazol-2-ylidene]silver(I) complex was structurally characterized by single-crystal X-ray diffraction. A series of new Ag-NHC complexes were screened for their in vitro antimicrobial activity against a variety of Gram-positive and Gram-negative bacteria as well as for their antifungal activity against a Candida albicans and Candida tropicalis.     

Review. Peering into an ATPase ion pump with single-channel recordings

In principle, an ion channel needs no more than a single gate, but a pump requires at least two gates that open and close alternately to allow ion access from only one side of the membrane at a time. In the Na+,K+-ATPase pump, this alternating gating effects outward transport of three Na+ ions and inward transport of two K+ ions, for each ATP hydrolysed, up to a hundred times per second, generating a measurable current if assayed in millions of pumps. Under these assay conditions, voltage jumps elicit brief charge movements, consistent with displacement of ions along the ion pathway while one gate is open but the other closed. Binding of the marine toxin, palytoxin, to the Na+,K+-ATPase uncouples the two gates, so that although each gate still responds to its physiological ligand they are no longer constrained to open and close alternately, and the Na+,K+-ATPase is transformed into a gated cation channel. Millions of Na+ or K+ ions per second flow through such an open pump-channel, permitting assay of single molecules and allowing unprecedented access to the ion transport pathway through the Na+,K+-ATPase. Use of variously charged small hydrophilic thiol-specific reagents to probe cysteine targets introduced throughout the pump's transmembrane segments allows mapping and characterization of the route traversed by transported ions.     

Encapsulation of the flavonoid quercetin with an arsenic chelator into nanocapsules enables the simultaneous delivery of hydrophobic and hydrophilic drugs with a synergistic effect against chronic arsenic accumulation and oxidative stress

Chronic arsenic exposure causes oxidative stress and mitochondrial dysfunction in the liver and brain. The ideal treatment would be to chelate arsenic and prevent oxidative stress. meso-2,3-Dimercaptosuccinic acid (DMSA) is used to chelate arsenic but its hydrophilicity makes it membrane-impermeative. Conversely, quercetin (QC) is a good antioxidant with limited clinical application because of its hydrophobic nature and limited bioavailability, and it is not possible to solubilize these two compounds in a single nontoxic solvent. Nanocapsules have emerged as a potent drug delivery system and make it feasible to incorporate both hydrophilic and lipophilic compounds. Nanoencapsulated formulations with QC and DMSA either alone or coencapsulated in polylactide-co-glycolide [N(QC+DMSA)] were synthesized to explore their therapeutic application in a rat model of chronic arsenic toxicity. These treatments were compared to administration of quercetin or DMSA alone using conventional delivery methods. Both nanoencapsulated quercetin and nanoencapsulated DMSA were more effective at decreasing oxidative injury in liver or brain compared to conventional delivery methods, but coencapsulation of quercetin and DMSA into nanoparticles had a marked synergistic effect, decreasing liver and brain arsenic levels from 9.5 and 4.8μg/g to 2.2 and 1.5μg/g, respectively. Likewise, administration of coencapsulated quercetin and DMSA virtually normalized changes in mitochondrial function, formation of reactive oxygen species, and liver injury. We conclude that coencapsulation of quercetin and DMSA may provide a more effective therapeutic strategy in the management of arsenic toxicity and also presents a novel way of combining hydrophilic and hydrophobic drugs into a single delivery system.     

Efflux of potassium ions from cells and spheroplasts of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> yeast treated with silver and copper ions

Silver ions induce the efflux of potassium from cells of the yeast Saccharomyces cerevisiae but have no such effect on spheroplasts. Copper ions and the natural fungicide 2-O-3-hydroxyhexanoyl-β-D-glucopyranosyl-(1→4)-(6-O-acetyl-β-D-glucopyranosyl-(1→16)-2,15,16-trihydroxyhexadecanoic acid) induce the efflux of potassium ions from both cells and spheroplasts of S. cerevisiae. Silver and copper ions inhibit the activity of the plasma membrane H⁺-ATPase during the treatment of both cells and spheroplasts. It is supposed that the inability of silver ions to stimulate potassium efflux from spheroplasts results from damage to some components of K⁺ transport systems during preparation of spheroplasts.