An Overview of the Options for Antimicrobial Hard Surfaces in Hospitals - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 145

￿ Does not promote clinically-significant resistance or reduced-susceptibility.
There is a risk that continuous sub-lethal exposure to microbes could occur on
AMS, and that this may lead to the development of resistance or reduced
susceptibility.
￿ Prevents biofilm formation. The ability to prevent the formation of biofilms,
or disrupt biofilms that have been formed, is a property of some oxidizing
disinfectants [ 61 ]. This property may be shared by AMS that exert antimicrobial
activity through oxidization. Also, modification of the physical structure of
surfaces may reduce biofilm formation.
￿ Compatible with current cleaning and disinfection products. The chemicals that
are used for regular cleaning and disinfection of the AMS should not interfere
with the antimicrobial activity of the surface, either in the short- or long-term.
￿ Safe. AMS must remain safe for regular and intimate contact with patients, staff
and visitors. AMS will sometimes come into contact with sensitive areas and
broken skin, and contact with the mouth and other mucous membranes should be
assumed possible.
￿ Low-cost. All AMS will be associated with a cost of some kind, which may be
absorbed into the manufacturing process for some products and coatings.

7.3 Assessing Antimicrobial Surfaces

7.3.1 In Vitro Activity

The first test of an AMS is an in vitro laboratory assessment of antimicrobial
activity. A number of test methodologies have been proposed. Historically, an
ISO standard test has been used (ISO22196), but test method is not appropriate
for testing surfaces specified for dry hospital surfaces since it is performed at high
humidity (100 %) and temperature (37 C) [ 62 ]. A standardized test has been
proposed that better reflects in-use conditions for dry hospital surfaces, but not
yet adopted widely [ 62 ]. Importantly, this methodology specifies an aerosol
deposition of microbes whereas other proposed methodologies specify the deposi-
tion of microbes in a liquid suspension. Testing the 'wet' deposition of microbes
may overestimate the antimicrobial potential of the surfaces, which would usually
be challenged with dry deposition in the real world. Another option is a United
States Environmental Protection Agency (EPA) test method for chemical agents
with residual activity [ 63 ], which has been modified and applied to metallic copper
(including alloys) [ 64 ] and copper oxide impregnated surfaces [ 65 ]. This method
also includes a test for the impact of abrasion on the activity of the surface.
Since standard testing methods have not been available, in vitro evaluations of
AMS have been performed using a wide range of parameters, principally, the test
organisms, concentration of the inoculum, method of deposition (including wet and
dry inocula), microbial recovery, contact times, temperature and relative humidity