An Overview of the Options for Antimicrobial Hard Surfaces in Hospitals - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 153

suggests that the cost of stainless steel door knobs was actually more than brass
alternatives with antimicrobial activity ($117 v $108) [ 80 ]. If clinical impact can be
demonstrated, then further studies evaluating the cost-effectiveness equation

are required.

7.4 Appraising the Options

7.4.1 Metals

A number of heavy metals have antimicrobial properties, which have been known
to mankind from antiquity [ 52 , 57 , 81 ]. The two metals that have been studied as
candidates for AMS are copper and silver.

7.4.1.1 Copper

Whilst the precise antimicrobial mechanism of action for copper remains a topic
for discussion, copper has redox potential, which generates reactive oxygen
species [ 57 ]. The in vitro antimicrobial activity of hard surfaces made of copper
and copper alloys has been evaluated in a number of studies, reviewed recently by
Grass et al. [ 57 ]. A wide range of vegetative bacteria and fungi have been evaluated,
with high-level log reductions possible, albeit sometimes with contact times that
are perhaps not useful for the healthcare setting. The concentration of copper in
the alloy being tested appears to be an important factor in determining efficacy.
A number of studies have evaluated the impact of copper surfaces on C. difficile
spores, with equivocal results [ 60 , 82 ]. One advantage of copper surfaces is their
ability to inactivate naked DNA [ 83 ], which may limit the spread of plasmids
containing resistance genes via the healthcare environment [ 84 , 85 ]. One in vitro
study of note repeatedly soiled and cleaned copper and stainless steel surfaces with
a suspension of S. aureus in bovine serum abumin over 5 days [ 86 ]. The result
indicated that the stainless steel surfaces were less susceptible to the build-up of
organic matter than the copper surfaces, which may influence antimicrobial activity
over time.
A number of studies have evaluated the potential for resistance or reduced
susceptibility to copper [ 87 - 90 ]. Whilst clinically-relevant resistance to copper
has not been identified associated with the introduction of copper AMS in the
healthcare setting, copper AMS do provide an environment that would select for
microbes with reduced copper susceptibility and may result in resistance in the
long-term.
Several in situ evaluations of the use of metallic copper surfaces (mainly copper
alloys) have been published (Table 7.2 ). A range of study designs have been used,
but these studies generally demonstrate a 1-2 log reduction in the level of contam-
ination on copper-containing AMS. Perhaps the most thorough study of the in situ