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34
The Dentist
January 2017
Disinfection and Decontamination
Practice disinfection
Regular disinfection of dental
practice surfaces is a key feature
of infection control, helping to
prevent the transfer of contamination in
between patients, and between patients
and practice staff. The wiping down of
surfaces between patient treatments is
recommended by the General Dental
Council (GDC).
There are a range of different
disinfectants with different active
ingredients available. The choice of
active ingredient affects the spectrum of
kill the disinfectant possesses (the range
of different microbial types that can be
killed). Other factors affecting selection
include safety; contact time (how long
the surface needs to be left for, following
disinfection); and format (with most
practices preferring pre-saturated wipes).
One of the most widely used types
of disinfectant is alcohol, because of
its wide spectrum of microbial kill.
Unlike some other types of disinfectants,
alcohol-based biocides can destroy the
bacteria responsible for tuberculosis
(Mycobacterium tuberculosis) and
for MRSA (antibiotic resistant forms
of Staphylococcus aureus), provided
they are applied with a suitable wiping
technique. An alternative disinfectant
class are quaternary ammonium
compounds ‘quats’, however these are
effective against a narrower range of
microorganisms. For example, quats
are ineffective against the tuberculosis
bacterium. They can also be affected
in the presence of hard water or when
acting and possesses a broad-spectrum
antimicrobial activity. When alcohols
are used in combination, such as IPA
and ethanol, the antimicrobial action
is arguably greater. This is because
IPA is slightly more efcacious against
bacteria, whereas ethanol is more potent
against viruses. The combination of the
two makes for an effective disinfectant
product.
An important factor with alcohols is
the concentration, with alcohols falling
within a concentration range of 60-80
per cent in water (volume/volume) being
the most efcacious (with a typical
commercial concentration of 70 per
cent).
Protein xation
Reference is sometimes made to
alcohols binding protein (like blood and
pus) on surfaces like stainless steel. This
can occur through a chemical reaction
called ‘xing’ (protein denaturation)
whereby the molecular shape of the
protein molecule alters.
However, to state that all alcohols
x protein to all surfaces in all
circumstances is an over-simplication.
Much of what has been written about
Dr Tim Sandle
is site microbiologist at Bio Products
Laboratory and a visiting tutor
with the School of Pharmacy and
Pharmaceutical Sciences, University
of Manchester.
Tim Sandle reviews the effectiveness of alcohol wipes.
in contact with materials like cotton or
gauze pads.
This article outlines the effective use
of alcohol based disinfectants within
the context of dental practice surfaces,
together with appropriate tips for their
application.
Alcohols
Alcohols are effective at eliminating
vegetative bacteria and viruses
from surfaces. The antimicrobial
effectiveness of alcohol is through
damage to bacterial cell membranes
and subsequent denaturation of
cellular proteins. Alcohols are effective
against microorganisms associated
with the skin, as well as pathogens
like Escherichia coli, together with M.
tuberculosis. With tuberculosis bacteria
in particular, alcohols are frequently
cited as the disinfectants of choice.
There are a range of different types
of alcohol (differentiated by molecular
weight) and not all of them are suitable
to be used as disinfectants. For example,
methanol has a weak bactericidal action
and would not be recommended for a
dental practice. A more effective alcohol
is isopropyl alcohol (IPA), which is fast
35
The Dentist
January 2017
Disinfection and Decontamination
protein xation is based on what
happens when protein is xed to a
microscope slide (here alcohol, at a
higher concentration of 80 per cent,
after an extended contact time, causes
proteins to precipitate). For protein
xation to occur the alcohol needs to
be in contact with the surface protein
for a prolonged period of time (in excess
of one hour) and for alcohols of a high
concentration (around 90 per cent) to
be used.
The extent that xation occurs also
varies depending upon the type of soil
and the type of surface (the degree
that it adheres to surfaces is dependent
upon electrostatic interactions with that
surface). For example, protein xation
that might occur with the surface
materials used as practice surfaces (such
as Formica) will differ to stainless steel
dental instruments. Differences relate to
strength of binding and likely contact
time, both of which are weaker (as with
binding) and shorter (as with contact
time) with practice surfaces. For this
reason, different protocols are needed
for the disinfection of instruments and
bench surfaces.
Furthermore, the forms of alcohol that
are sometimes cited as being of concern
are not industry standard. Alcohols
diluted to 60-80 per cent are prepared
so that the disinfection activity takes
place more slowly, which allows the
alcohol to enter the cell. Moreover,
alcohols in studies shown to be protein
xing invariably do not contain added
surfactant.
Importantly protein xation is not
considered to be a concern with
alcohol based wipes, when applied to
the common types of surface found in
dental practices. This is provided that:
The area which is exposed to blood is
disinfected promptly;
The alcohol is applied using a wipe
(either pre-saturated or using a spray and
wipe);
More than one wiping action is used
(typically a surface will be wiped at least
twice);
The disinfected surface is left for a
recommended time (‘contact time’)
before use. Typically this is one minute,
although the time will be recommended
by the manufacturer.
These factors should be assessed
against an appropriate disinfectant
efcacy standard provided by the
manufacturer of the product. A suitable
standard for wipes is EN 13697:2015.
Disinfectant efcacy tests are conducted
under simulated ‘clean’ and ‘dirty’
conditions. Dirty conditions are
designed to simulate the presence of
‘soil’ (like grease or blood protein).
When reviewing studies it is important
that the soil used is representative of
the types found within the practice
rather than a substitute soil like bovine
albumin. Another point to note is the
contact time. An example of a study
using alcohol wipes featured in the
October 2014 edition of The Dentist;
this study demonstrated that industry
standard alcohol wipes are effective for
killing the microorganisms of concern in
the practice setting.
Cleaning and wiping
Where soil is present on a surface,
cleaning is required prior to disinfection
(or, optimally, a disinfectant that
contains a detergent is used). This is
because many disinfectants have a
limited capacity to penetrate soil and
make contact with the microbial cell.
Therefore, any remaining concerns with
protein can be further overcome when
alcohol-based disinfectants containing
surfactants are used (as is the case
with some proprietary alcohol wipes.)
Here the surfactant reduces the surface
tension and prizes-apart the protein
from the microorganisms, allowing
the disinfectant to make contact with
the microorganisms and destroy the
microorganism.
In addition, microorganisms bound
to surfaces (such as the dental practice
work surface) behave differently to
microorganisms in a free-oating state
(such as in water) and are far more
resistant to antimicrobial agents. This
is because slime produced by bacterial
communities prevents the perfusion
of biocides to bacterial cell targets.
To overcome this, effective wiping in
at least two motions, is needed. This
means the combination of a disinfectant-
detergent plus the physical force of
wiping are the key requisites for effective
disinfection.
Summary
This article has provided an overview
of the efcacy of alcohol-based
disinfectants, considering the typical
types found within the dental practice.
One concern raised with alcohols is
the phenomenon of protein xation
and the effect of this on the ability of
the disinfectant to achieve adequate
microbial kill. This remains theoretical
due to the timescales required for
xation, which are unlikely to occur
in practical situations; as a safeguard,
the use of effective wiping techniques
and the selection of alcohol based
disinfectants that contain added
surfactants, will overcome any risk of this
effect. Taking account of these factors
leads to the conclusion that alcohol
based disinfectants are among the most
appropriate for use in the dental setting.
References available on request.
Could you be the ‘schülke Infection Prevention & Control Practice of 2017’?
You can now register for the 2017 schülke Infection Prevention & Control Practice of the Year awards. schülke,
specialists in infection prevention and control, is working in partnership with The Dentist to recognise the
commitment of dental practices to infection prevention and control. The award is open to all dental practices
across the UK and the winning team will receive their trophy at Dental Showcase at NEC, Birmingham in October.
Registration could not be simpler, just return the freepost card in this issue of The Dentist to register your practice
for the awards, or email your contact details to ipcaward.sm@schuelke.com. Every practice who registers will
receive a short questionnaire to complete. Shortlisted practices will be visited and interviewed by a member of The
Dentist editorial team.
This year the winning team will receive an autoclave worth £5,000 from NSK, as well as a trip to BDIA in
Birmingham on 20th October, to be presented with their winner’s trophy and certicate.