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Applied and Environmental Microbiology, January 2001, p. 198-205, Vol. 67, No. 1
Food Safety Laboratory, Department of Food
Science,1 Department of Population
Medicine and Diagnostic Sciences,3 and
Department of Food Science,4 Cornell
University, Ithaca, New York 14853, and Cornell University
Cooperative Extension, New York Sea Grant, State University of New
York, Stony Brook, New York 11794-50022
Received 18 April 2000/Accepted 14 September 2000
We have applied molecular approaches, including PCR-based detection
strategies and DNA fingerprinting methods, to study the ecology of
Listeria monocytogenes in food processing environments. A
total of 531 samples, including raw fish, fish during the cold-smoking process, finished product, and environmental samples, were collected from three smoked fish processing facilities during five visits to each
facility. A total of 95 (17.9%) of the samples tested positive for
L. monocytogenes using a commercial PCR system (BAX for
Screening/Listeria monocytogenes), including 57 (27.7%)
environmental samples (n = 206), 8 (7.8%) raw
material samples (n = 102), 23 (18.1%) samples
from fish in various stages of processing(n = 127), and 7 (7.3%) finished product samples (n = 96). L. monocytogenes was isolated from 85 samples
(16.0%) using culture methods. Used in conjunction with a 48-h
enrichment in Listeria Enrichment Broth, the PCR system had
a sensitivity of 91.8% and a specificity of 96.2%. To track
the origin and spread of L. monocytogenes, isolates were
fingerprinted by automated ribotyping. Fifteen different ribotypes were identified among 85 isolates tested. Ribotyping data
established possible contamination patterns, implicating raw
materials and the processing environment as potential sources of
finished product contamination. Analysis of the distribution of
ribotypes revealed that each processing facility had a unique contamination pattern and that specific ribotypes persisted in the environments of two facilities over time (P
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.1.198-205.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Molecular Studies on the Ecology of Listeria
monocytogenes in the Smoked Fish Processing Industry
0.0006). We conclude that application of molecular approaches can
provide critical information on the ecology of different L. monocytogenes strains in food processing environments. This
information can be used to develop practical recommendations for
improved control of this important food-borne pathogen in the food industry.
*
Corresponding author. Mailing address: Department of
Food Science, 412 Stocking Hall, Cornell University, Ithaca, NY 14853. Phone: (607) 254-2838. Fax: (607) 254-4868. E-mail:
mw16{at}cornell.edu.
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