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Applied and Environmental Microbiology, June 2001, p. 2586-2595, Vol. 67, No. 6
Danish Institute for Fisheries
Research, Department of Seafood Research, Søltofts Plads,
Technical University of Denmark, DK-2800 Kgs.
Lyngby,1 Department of Veterinary
Microbiology. The Royal Veterinary and Agricultural University,
DK-1870 Frederiksberg,2 and Danish
Veterinary Laboratory, DK-1790 Copenhagen V,3
Denmark
Received 29 December 2000/Accepted 12 March 2001
The contamination routes of Listeria monocytogenes in
cold-smoked salmon processing plants were investigated by
analyzing 3,585 samples from products (produced in 1995, 1996, 1998, and 1999) and processing environments (samples obtained in 1998 and 1999) of two Danish smokehouses. The level of product contamination in
plant I varied from 31 to 85%, and no L. monocytogenes was found on raw fish (30 fish were sampled). In
plant II, the levels of both raw fish and product contamination varied
from 0 to 25% (16 of 185 raw fish samples and 59 of 1,000 product
samples were positive for L. monocytogenes). A total
of 429 strains of L. monocytogenes were subsequently
compared by random amplified polymorphic DNA (RAPD) profiling, and 55 different RAPD types were found. The RAPD types detected on the
products were identical to types found on the processing equipment and
in the processing environment, suggesting that contamination of the
final product (cold-smoked salmon) in both plants (but primarily in
plant I) was due to contamination during processing rather than to
contamination from raw fish. However, the possibility that raw fish was
an important source of contamination of the processing equipment and
environment could not be excluded. Contamination of the product
occurred in specific areas (the brining and slicing areas). In plant I,
the same RAPD type (RAPD type 12) was found over a 4-year period,
indicating that an established in-house flora persisted and was not
eliminated by routine hygienic procedures. In plant II, where the
prevalence of L. monocytogenes was much lower, no RAPD
type persisted over long periods of time, and several different
L. monocytogenes RAPD types were isolated. This
indicates that persistent strains may be avoided by rigorous cleaning
and sanitation; however, due to the ubiquitous nature of the organism,
sporadic contamination occurred. A subset of strains was also typed by
using pulsed-field gel electrophoresis and amplified fragment length
polymorphism profiling, and these methods confirmed the type division
obtained by RAPD profiling.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.6.2586-2595.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Elucidation of Listeria monocytogenes
Contamination Routes in Cold-Smoked Salmon Processing Plants
Detected by DNA-Based Typing Methods
*
Corresponding author. Mailing address: Danish Institute
for Fisheries Research, Department of Seafood Research, Søltofts
Plads, Technical University of Denmark, Bldg. 221, DK-2800 Kgs. Lyngby, Denmark. Phone: 45 45 88 33 22. Fax: 45 45 88 47 74. E-mail:
bfv{at}dfu.min.dk.
Applied and Environmental Microbiology, June 2001, p. 2586-2595, Vol. 67, No. 6
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.6.2586-2595.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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