Publisher Summary This chapter discusses antimicrobial activity and action of silver. Silver and its compounds have long been used, in one form or another, as antimicrobial agents. The silver compound of major therapeutic interest at the present time is silver sulphadiazine. Many in healthcare know that other silver compounds are still in use. It is worth stating that the treatment of ophthalmia neonatorum was revolutionized by the instillation of silver derivatives into the eyes of new-born sufferers. Several factors influence the antimicrobial activity of silver salts. Silver has a marked tendency to adsorb to surfaces and bactericidal activity is reduced in the presence of phosphates, chlorides, sulphides and hard water. Activity is increased as the temperature is raised and is pH-dependent, increasing with increasing pH. Sodium thioglycollate has been recommended as a suitable neutralizing agent for use in bactericidal testing although other SH compounds also fulfil this role. Silver, one of the native metals and second only to gold in its stability amongst the metals of antiquity, has provided several therapeutic agents which have been employed since the beginning of recorded history. These agents range from the metal itself, its salts and complexes with proteins and other macromolecules to the latest, silver sulphadiazine (AgSD).

Antimicrobial activity and action of silver

Silver-ion-mediated reactive oxygen species generation affecting bactericidal activity.

Disinfection due to copper or silver ions may result from action at the cell or capsid protein surface or on the nucleic acid of cells or viruses. Metals may alter enzyme structure and function or facilitate hydrolysis or nucleophilic displacement. The means by which cells may reduce the toxic effect of metal ions include: biomethylation, complexation with metallothionen, development of efflux pumps, the binding of metal ions to cell surfaces, and the removal of metal ions by precipitation. The phenomenon of “multiplicity of reactivation” may reduce the effect of a disinfectant on a virus by allowing a clump of partially inactivated viruses to produce a productive infection in a susceptible cell. Conditions which may affect metal ion‐biomolecule interaction include: pH, ionic strength, temperature, dissolved oxygen, presence of interfering substances or light, the chemical form and valency of the metal ion, and the condition of the microorganisms.

The Molecular Mechanisms of Copper and Silver Ion Disinfection of Bacteria and Viruses

The molecular mechanisms of copper and silver ion disinfection of bacteria and viruses

Postoperative implant-associated infection is still an unresolved and serious complication in modern surgery. Antibacterial and biocompatible surfaces could both reduce infection rates and promote tissue integration. In this respect, a comparative study of the antibacterial as well as the biocompatible potential of different metal ions in vitro is presented. The assays used were growth inhibition tests with different metal salts carried out with tissue cells and bacteria under corresponding culture conditions. Additionally, in vitro tests in direct surface contact with tissue cells and bacteria onto a novel copper containing sol-gel derived titanium dioxide coating (Cu-TiO2) and a fourfold Cu-TiO2 coating were performed. The values were compared to a non-filled titanium dioxide coating and standard Ti6Al4V alloy. SEM-investigations were performed to approve the results of the in vitro tests. Among Ag+, Zn2+, Co2+, Al3+ and Hg2+, the growth inhibition tests revealed an outstanding position of copper ions as antibacterial but nevertheless bio-tolerant additive. These results were affirmed by the cell tests in direct surface contact and SEM-investigations, where best cell growth was found on the Cu-TiO2 coatings. Highest antibacterial properties with a tolerable cytocompatibility could be observed on the fourfold Cu-TiO2 coatings. Consequently, surfaces with custom-tailored antibacterial properties may be established and could be of particular interest in revision and tumor arthroplasty.

A novel antibacterial titania coating: metal ion toxicity and in vitro surface colonization.

Increasing use of silver in the treatment of water has necessitated an examination of microbiological methods for the measurement of silver inactivation of microorganisms. Three common agar media were tested for their ability to neutralize the bacteriostatic effects of silver. Results suggested that growth media differed in their neutralizing capacity; that is, the non-inhibitory media tryptone glucose agar and Trypticase soy agar showed more neutralizing capacity than eosin methylene blue agar. Furthermore, the neutralizing effect appeared to be a function of the soluble component of the media and not of the agar itself.

B Rosenberg

Papers

Reversal of the silver inhibition of microorganisms by agar.