Biocidal Mechanisms of Metallic Copper Surfaces - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 110

Some recent findings suggest an alternative mechanism responsible for the primary
toxic effects of copper in vivo. A first evidence of such is that the majority of copper
inside the cell is bound to biomolecules, while free copper is at extremely low levels
or even nonexistent, thus making the Fenton chemistry and sulfhydryl depletion
very unlikely mechanisms [ 10 ]. Another study by [ 51 ] showed that E. coli cells
grown without copper are more sensitive to killing by hydrogen peroxide than
E. coli pretreated with copper. In addition, copper decreases the rate of DNA
damage induced by hydrogen peroxide. The authors suggested that copper exerts
its toxicity by mechanisms other than oxidative stress. Furthermore, [ 50 ] showed
in vivo as well as in vitro that a rise of intracellular copper concentrations is
associated with the displacement of iron from iron-sulfur clusters. For example, it
was shown that copper specifically damaged the iron-sulfur clusters of various
dehydratases involved in branched amino acid biosynthesis from E. coli cells.
Further investigation in this field is needed, in order to have a clear conception on
the mechanism of copper-induced toxicity in cells.
Without copper-detoxifying mechanisms, cells suffer copper-induced toxicity
that might compromise survival. Moreover, another challenge presents a severe
stress for bacterial survival - toxicity caused by contact to metallic copper. Knowl-
edge related to this so-called “contact-killing” [ 35 ] by metallic copper surfaces, is
reported in the following section.
6.3 Metallic Copper Surfaces as a Biocidal Tool
6.3.1 Quick Cell Inactivation by Metallic Copper Surfaces
The effectiveness of copper surfaces in bacteria killing was investigated both in
laboratory and hospital conditions. Generally, two major inoculation techniques
were employed to study metallic copper's antimicrobial properties: the wet and
dry methods, imitating different environments of bacteria surface contamination.
The first ever described method explores the antimicrobial activity of metallic
copper surfaces against cells suspended in a buffer solution (wet method). This
inoculation technique was first developed by [ 29 ] and then further optimized by
[ 93 ] to the method that is widely used today. In the presence of a buffer solution
cells are not directly in contact with the surfaces but instead suspended away from
the metallic copper (e.g. [ 29 , 65 , 66 , 93 , 94 ]). The wet method mimics moist
environments, such as food processing, public baths, water conservation, pipelines,
and bathrooms, where droplets containing germs fall on top of surfaces and can be
picked up by a person. In the early studies the bactericidal property of copper
surfaces was screened against panel of microorganisms. In 2004 Fa´ndez [ 29 ]
demonstrated that copper surfaces are able to reduce bacterial counts of
S. enterica and Campylobacter jejuni - two notorious human pathogens mainly
transmitted by food ingestion. This study was the first peer-reviewed publication