Avoid hysteria about listeria
April 1st 2012
Cleanliness in any facility is important to protect product, reputation and revenue.
However the need for effective cleaning regimes in food manufacturing facilities
goes way beyond this, potentially being a matter of life and death. Neil Brown,
technical director of Hygiene Group explains how en effective cleaning, disinfection
and maintenance programme can help to mimise risks
Contamination during processing can cause huge problems
for manufacturers, but can cause an even bigger problem for
the consumer. Among the worst of these contaminants is
Listeria. So common that it cannot be eradicated completely, there
are measures that can be taken to ensure levels are reduced to the
point where it is unlikely to cause infection and disease.
Listeria is a rod-shaped bacterium, widely found wherever there is
standing water in both food factories and the wider environment.
Transferred easily, Listeria can be carried into manufacturing facilities
on equipment, or on the boots and clothing of operatives. While most
of the thousands of species of Listeria are of no clinical significance in
humans, two or three serotypes of monocytogenes are commonly
implicated in the human illness listeriosis.
The symptoms of listeriosis range from those that we associate
with a severe cold or mild food poisoning to septicaemia. Listeriosis
can be life-threatening, particularly among pregnant women and
people with reduced immunity such as the elderly and the very
young. Death rates of 20 to 30 per cent are often quoted.
Facilities which process liquids such as unpasteurised milk are
probably the most susceptible to Listeria contamination, as are
facilities that wash produce and as a result have excess water pooling.
Food is self-protecting to a point, particularly food with a high salt or
sugar content. But food with high water content, such as cooked
meats, can be high-risk even when refrigerated as Listeria can grow in
Time to get dry?
Keeping areas dry and eliminating the presence of unnecessary
water can significantly reduce the risk of contamination. Rinse water
left on the floor and pooling inside equipment should be cleaned up
where possible. However, standing water inside drains can harbour
Listeria, and this cannot be taken away. It is important, therefore, that
careful cleaning processes are implemented to minimise the risk,
along with terminal disinfection.
Drains and covers should be cleaned carefully and then coated
with a foam disinfectant which can be left to work. Floors should be
cleaned and dried carefully to avoid water pooling.
Because of their physical characteristics, Biofilms on surfaces
harbour many microorganisms, including Listeria monocytogenes,
and are particularly difficult to clean, requiring a particular
combination of chemicals to remove.
Effective cleaning then needs to be followed by total coverage with a
fine spray of disinfectant, ensuring that this covers and penetrates the
entire surface. Residues of disinfectants left on the top of sprayer tips
and bottles need to be removed as, when dry, those left by quats and
amphoterics can actually support microbial growth, so adding
another source of infection.
While chiller evaporators need frequent cleaning, the condensate
lines are easily forgotten. After cleaning the body of the evaporators,
biocides should be pumped into the condensate tray and allowed to
drain through the condensate line. It is even better if the lines can be
temporarily blocked, to extend contact time.
Another forgotten place that can harbour Listeria is the very fabric
of the building. Walls and dividers that sandwich insulation, if
damaged, can absorb contaminated water from the floor and lift it as
high as three to four feet within the fabric. The walls then become a
reservoir for infection, and this cannot be cleaned. It is therefore not
just the cleaning that is important, but the maintenance of the
Despite the press hype surrounding well publicised cases of
Listeriosis in humans, the bacterium can be destroyed easily with
biocides. The potential risks in food factories, though considerable, can
be minimised relatively simply through planning and implementing an
effective programme of cleaning,
disinfection and maintenance.
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