will be found, but does not necessarily
indicate an unsafe condition. Likewise,
finished product testing is not likely to
be as sensitive to detecting potential
contamination as environmental
monitoring. However, environmental
monitoring programs should be
designed to find harborages, not just
meet customers’ expectations for Listeria
testing. Microbiologists skilled in
Listeria detection should be consulted to
develop a series of rotating monitoring
points to detect when Listeria has
invaded the processing area, and these
should be tested vigorously (e.g., avoid
wasting efforts on smooth surfaces; swab
weld joints and hidden surfaces instead).
Initial findings of Listeria spp. should
lead to more aggressive cleaning and
sanitizing in the area and retesting. If
retesting yields negative findings, then
the operation should go back to normal
monitoring of the area. If retesting yields
positive findings, then the Listeria may
have found a harborage point, which
needs to be found through extensive
testing and eliminated like any pest.
Listeria is a pervasive microorganism and
has found harborage in unlikely places,
such as hollow ladder rungs, hollow
conveyor rollers, facility walls and chill
The tragic outbreak last year
demonstrated that packinghouses might
be as vulnerable to Listeria harborage
and product contamination as fresh-cut operations. While Listeria is not
likely to become entrenched in dry
environments, operations or equipment
that are routinely wet are vulnerable.
Additionally, packinghouses that are not
routinely held at the cold temperatures
of fresh-cut operations can be even
more vulnerable; while Listeria has a
competitive advantage because it can
survive and grow in cold environments,
it likes warmer environments even more.
For more information about L.
monocytogenes and environmental
monitoring programs, operations should
consult;FDA’s;Bad Bug Book, 3;FDA’s
Listeria guidance for industry, or a
commercial laboratory experienced in
Listeria and environmental testing. n
David E. Gombas, Ph.D., is the senior vice
president, food safety and technology, at the
United Fresh Produce Association.
2. Tompkin, R.B., V.N. Scott, D. T. Bernard, W.H.
Sveum and K.S. Gombas. 1999. Guidelines to
prevent post-processing contamination from
Listeria monocytogenes. Dairy Food Environ
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