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Sterilisation
has become a key process since the introduction of good laboratory
practice. The complete removal of viable microbiological organisms,
viruses and bacterial spores is now routine in industries
as diverse as healthcare (including pathology), biotechnology,
pharmaceuticals, food and dairy, agriculture and horticulture,
industrial research, water and environment, and brewing.
There are a
variety of different ways of achieving sterility, including
chemical soaks and ionising radiation, but generally steam
is considered the best option for those applications that
are not heat-sensitive. Steam autoclaves saturate the air
with enough dry heat to efficiently transfer 2500 joules per
gram of heat onto a micro-organism, thus raising its temperature
to a level at which it is destroyed. The process is inexpensive,
doesn't leave behind toxic residues, as chemicals are prone
to do, and can, when properly validated, be 100 per cent effective.
The sort of
loads that need sterilisation vary depending on the activities
in the facility, but generally include growth media and fluids,
wrapped and unwrapped instruments, laboratory utensils and
equipment, and fabrics and textiles. In recent years there
has also been an increased demand, under duty-of-care legislation,
for the safe sterilisation of potentially bio-hazardous material
prior to disposal.
Some well-known
types and forms of contaminated waste arise from microbiological
and clinical facilities; however, in recent years there has
been a significant increase in contaminated waste from agricultural
and horticultural research. This is due, in part, to using
GM technology as tools in plant and microbiological studies.
The recent surge of knowledge on plant gene functions would
not have been possible without the use of transgenic plants
in molecular genetic studies, but using GM technology in this
way means that strict procedures for waste disposal must be
employed by the research organisation to comply with legislation.
No organisation
knows the regulations involved better than the John Innes
Centre (JIC) in Norwich, one of the UK's leading independent
centres of excellence in plant science and microbiology. Among
JIC's facilities are thousands of square metres of containment
glasshouses that accommodate the majority of the Centre's
containment-based research, and every one meets strict industry
regulations, which includes the use of sterilisation in waste
disposal procedures. Stephen Andrews, Section Head of Mechanical
and Electrical Services in the Department of Building and
Engineering Support Services (BESS), explained: "We must
use autoclaves to destroy the soil samples and general waste
that is generated inside the containment glasshouses. It is
a critical process that forms part of our licensing agreement
with DEFRA for carrying out containment-type studies."
An ordinary
single door laboratory autoclave isn't sufficient for disposal
in a containment facility, as the volumes of waste are large
and must be completely contained until destruction, so double-door
autoclaves must be used instead. These have interlocking doors
that allow the outer door to be opened only after completion
of the sterilising cycle, thus preventing the simultaneous
opening of both doors and possible contamination.
Although there
were existing autoclaves already performing these tasks in
the greenhouses, the Centre wanted to update them to achieve
a more efficient operation and increase cycle times. "We
decided to purchase two Astell Scientific large Double
Door Square Section Units with Logi Touchscreen Controllers because we liked the flexibility of
the design and had good experiences of using the Company's
equipment in the past. The autoclaves were custom-designed
to fit into the existing wall openings after removal of the
old machines, and had an SPF Bacterial Seal fitted around
them where they fixed into the wall so a complete barrier
between the "dirty" and "clean" sides
of the process was formed to prevent bacterial migration.
The waste is fed into the autoclaves from the "dirty"
side before being sterilised and removed on the "clean"
side for disposal."
Perhaps the
single most important issue facing the team that maintain
the containment glasshouses is quality assurance. Sterilisation
and disposal procedures must be fully documented and validated
to ensure that these defined processes are consistently carried
out and, if necessary, are traceable. Generally speaking,
the validation
of autoclaves is usually performed under three specific circumstances;
after their installation, as part of regular maintenance and
immediately after any significant changes are made that could
affect the sterilisation process. The latter includes repairs
and recalibrations
of the autoclave and any changes to the sterilisation process
itself.
For validation
procedures, the Astell Scientific autoclaves at John Innes
use a 12-point chart recorder and probes, one of which is
UKAS calibrated and serves as the reference for all the others.
All the probes are inserted into the load through a thermocouple
entry port in the chamber wall, a standard feature on all
Astell machines, before the cycle is started.
"In order
to demonstrate compliance with DEFRA's stringent requirements
on 'good practice', the Centre performed a 12-point thermocouple
validation after the autoclaves were installed to set a baseline
and demonstrate that they were capable of achieving the necessary
temperature/time requirements throughout the load. We also
use a "thermotag" interrogator to demonstrate that
temperatures are reached on a regular basis. By keeping records
of all of these tests, we can demonstrate to the DEFRA inspectors
when they visit that we are following the tenets of good practice."
The autoclaves
are already having a significant positive effect on the disposal
procedures and workloads at JIC: "Because the new autoclaves
have a much lower steam consumption than our previous models,
we can run two autoclaves and a steam lance simultaneously,"
explained Stephen. "Combined with the faster cycle times
which have increased our throughput, the number of hours taken
to dispose of the waste has decreased considerably. Normally,
it is a continuous five-day, every day process, but since
the installation of the autoclaves we now only spend three days a week doing
it instead." |
