The contaminationsites in different foodprocessingplants for the mostpart are
the same,with processingmachines standingout. It has beenshownby molecular
typing that identicalL. monocytogenesgenotypescan be foundin the processing
machinesand the productthat has beenmanipulatedby that machineor in the
productwaste of such machines. Thesefindingsstronglyindicatethat the pro-
cessing machineshavetransferredthe contaminationto the products(Nesbakken
et al., 1996;Autioet al., 1999;Suihkoet al., 2002;Lunde¬net al., 2003a).
Processingmachinesthat are complex and difficultto take apartand therefore
sanitizehave been found problematic (Table 33.3). In particular, brining
machinesand particularly recirculating briningmachinesare difficult to clean
(Autioet al., 1999; Greeret al., 2004).Otherchallenging processingmachines
are packingmachines, freezers and conveyors (Autioet al., 1999;Miettinenet
al., 1999;Hoffmanet al., 2003)and machines that reduce product size,e.g.
slicers and dicers. The difficulty of eliminating L. monocytogenes from
processingmachinesis wellillustratedin the casewhere the contamination
was transferredwitha sanitizeddicingmachine fromone plantto another. The
contamination was causedby a persistentstrain,whichhad an increased ability
Table33.3 Listeriamonocytogenescontaminationsitesin foodprocessingplants
Contaminationsite Reference
Processingenvironment Autioet al.(1999),Chasseignauxet al.(2001),
Berranget al.(2002)
Cutter Chasseignauxet al.(2001)
Tumblingmachine Sameliset al.(1998),Samelisand Metaxopoulos,1998)
Cuttingtable Nortonet al.(2001)
Trimming Eklundet al.(1995),Johanssonet al.(1999)
Briningmachine Autioet al.(1999),Johanssonet al.(1999),
Miettinenet al.(2001a)*
Briningsolution Eklundet al.(1995),Autioet al.(1999),Nortonet al.(2001)
Skinningmachine Autioet al.(1999),Suihkoet al.(2002),
Miettinenet al.(2001b)
Slicingmachine Autioet al.(1999),Johanssonet al.(1999),
Suihkoet al.(2002)
Dicingmachine Lunde¬net al.(2002)
Conveyorbelt Salvatet al.(1995),Giovannacciet al.(1999),
Miettinenet al.(2001b)
Coldsmoker Nortonet al.(2001)
Chillingmachine Miettinenet al.(2001b)
Cooler Hoffmanet al.(2003)
Freezer Pritchardet al.(1995),Lunde¬net al.(2003a)
Mould Jaquetet al.(1993),Salvatet al.(1995)
Packagingmachine Johanssonet al.(1999),Miettinenet al.(1999),
Lunde¬net al.(2003)
Milkfiller Pritchardet al.(1995)
Brinepre-filter Pritchardet al.(1995)
*Listeriaspp.
546 Handbookof hygiene controlin the foodindustry