Plant Cleaning and Sanitation 295the dicing machine, L. monocytogenes origi-
nally found in plant A was soon also found
in plants B and C, and was frequently iso-
lated from the diced products. This particular
strain of L. monocytogenes proved to have
a high level of adherence to stainless steel
surfaces and a signifi cant resistance to
QUAT.
Research and experience indicates that L.
monocytogenes tolerates well various stress
factors that it encounters in food - processing
plants and has a very good ability to attach
to different surfaces and thus to persist in
food plants for years (Senczek et al. 2000 ;
Lund é n et al. 2003 ). Insuffi cient manual
scrubbing during the cleaning process and an
inadequate disinfection have been linked to
the presence of L. monocytogenes in fi nished
products.
Sanitizers that are most effective against
L. monocytogenes are quaternary ammonium
compounds (QUATs), chlorine solutions,
and products containing peroxyacetic acid
(Table 15.2 ).
Rotating sanitizers periodically is usually
a good practice, as it will provide more
effectiveness against L. monocytogenes as
well as other bacteria. The frequency of
cleaning and sanitizing the equipment and
the environment of a plant depends upon the
experience and the microbiological data.
Suggested frequencies are shown in Table
15.3.
It has been shown that L. monocytogenes
can become established and persist in fl oor
drains. Therefore, drains should be cleaned
and disinfected in a manner that prevents
contamination of other surfaces in the room.
Solid forms of disinfectants (e.g., blocks of
QUATs) can be placed in drains to help
control bacterial growth. Floor drains should
not be cleaned during production. High -
pressure hoses should not be used to clear or
clean a drain, as aerosols will be created that
spread contamination throughout the room.
Employees who have been cleaning drains
should not contact or clean food contact sur-
faces without changing clothes and washingwater, silage, and many other environmental
sources. Listeriosis may develop in birds,
animals, and humans. L. monocytogenes is
especially pathogenic to high - risk popula-
tions, including newborns, pregnant women,
elderly, and immunocompromized persons.
The symptoms of the disease include fever,
chills, headache, abdominal pain, and
diarrhea.
Epidemiological studies have confi rmed
that meat products have been involved in
sporadic cases and outbreaks of listeriosis in
many countries. Contamination of ready - to -
eat (RTE) meat and poultry products by L.
monocytogenes has represented a major
source of foodborne illness in the United
States in recent years. The lethality treatment
received by many processed RTE meats and
poultry products generally eliminates the
pathogen; however, when the disinfection is
inadequate, products can be contaminated by
exposure to the environment after the lethal-
ity treatment, during peeling, slicing, and
repackaging operations. In general, the con-
tamination sites in meat - and poultry -
processing plants are mainly the food - contact
surfaces and processing machines: convey-
ors, slicers, peelers, dicers, and brining and
packaging machines.
Experience in cold - smoked pork products
processing establishments indicates that con-
tamination of the fi nished product appears to
mostly be due to L. monocytogenes strains
already present in the plant environment
(B e ̄ rzi n ̧ š et al. 2007 ). This experience con-
fi rmed the results obtained by other authors
(Norton et al. 2001 ; Hoffman et al. 2003 ).
Both persistent and nonpersistent strains
were isolated from pork products produced
in seven different plants.
Previous studies have shown that persis-
tent L. monocytogenes strains can often be
found in various parts of food processing
equipment. Lund é n et al. (2002) evaluated
the possibility of transferring persistent L.
monocytogenes contamination from one
plant to another with a dicing machine for
cooked meat products. After the transfer of