sAni TATion
cheeses, the lactic acid bacteria are natural inhibitors. Nevertheless, the 2012
U.S. Food and Drug Administration/
Health Canada draft risk assessment
found that the risk of listeriosis from
soft-ripened cheeses made with raw milk
is estimated to be 50 to 160 times higher than that from soft-ripened cheese
made with pasteurized milk. 12
L. monocytogenes is persistent in
fish and shellfish processing plants.
Cross-contamination can originate in
external and internal sources. In British Columbia, more fish facilities than
dairy and meat facilities had FCS and
RTE fish foods contaminated with
Listeria spp., and increased inspection is
recommended. 13 In Scandinavia, there
is a high prevalence of contaminated
cold-smoked and gravid fish that have
caused outbreaks. 14 Sweden plans to
halve the prevalence of L. monocytogenes
in these products by the end of 2015.
Research has shown that a combination of any two of nisin, lysozyme and
e-polylysine antimicrobials effectively
inhibit growth of L. monocytogenes in
RTE seafood. However, some traditional
processes may also discourage the survival of L. monocytogenes. For instance,
the pathogen decreases during storage
in vinegar-marinated sushi rice with raw
salmon and halibut. 15 Although electrolyzed oxidizing (EO) water has not
been shown to be effective against L.
monocytogenes on fish surfaces directly,
removal of fish residue from processing
equipment such as conveyor belts and
slicing machines and their exposure to
EO water could assist in reducing biofilm formation. 16
Sanitation
In processing plants, both FCS and
non-FCS can be important reservoirs
for Listeria spp. In fact, a false sense of
security can occur when only FCS are
tested, since the main reservoirs can
be as varied as wet floors, drains, shoe
soles, equipment brackets and stair
treads. In the 2011 cantaloupe outbreak,
there was condensation from cooling
systems draining directly onto the floor;
poor drainage, resulting in water pool-
ing around the food processing equip-
ment; difficult-to-clean food process-
ing equipment; and no antimicrobial
solution in the water used to wash the
cantaloupes. Sanitary equipment and
plant design are crucial for controlling
contamination. Because of a study of
a cooked frozen chicken meat opera-
tion that showed Listeria spp. was most
frequently recovered from the liquid
nitrogen chiller exhaust pipe, the metal
detector conveyor belt and the freezer
drain, the plant’s cleaning and sanitiz-
ing procedures were revised and strictly
implemented to reduce and eliminate
the sources of Listeria contamination. 17
In retail deli operations, hands and
gloves have been identified as important
potential contamination sources. Patho-
gen transfers are likely to occur from
non-FCS (floor drains, walk-in cooler