Listeria monocytogenes Contamination Patterns for the Smoked Fish Processing Environment and for Raw Fish

Reliable data on the sources of Listeria monocytogenes contamination in cold-smoked fish processing are crucial in designing effective intervention strategies. Environmental samples (n = 512) and raw fish samples (n = 315) from two smoked fish processing facilities were screened for L. monocytogenes, and all isolates were subtyped by automated ribotyping to examine the relationship between L. monocytogenes contamination from raw materials and that from environmental sites. Samples were collected over two 8-week periods in early spring and summer. The five types of raw fish tested included lake whitefish, sablefish, farm-raised Norwegian salmon, farm-raised Chilean salmon, and feral (wild-caught) salmon from the U.S. West Coast. One hundred fifteen environmental samples and 46 raw fish samples tested positive for L. monocytogenes. Prevalence values for environmental samples varied significantly (P < 0.0001) between the two plants; plant A had a prevalence value of 43.8% (112 of 256 samples), and plant B had a value of 1.2% (3 of 256 samples). For plant A, 62.5% of drain samples tested positive for L. monocytogenes, compared with 32.3% of samples collected from other environmental sites and 3.1% of samples collected from food contact surfaces. Ribotyping identified 11 subtypes present in the plant environments. Multiple subtypes, including four subtypes not found on any raw fish, were found to persist in plant A throughout the study. Contamination prevalence values for raw fish varied from 3.6% (sablefish) to 29.5% (U.S. West Coast salmon), with an average overall prevalence of 14.6%. Sixteen separate L. monocytogenes subtypes were present on raw fish, including nine that were not found in the plant environment. Our results indicate a disparity between the subtypes found on raw fish and those found in the processing environment. We thus conclude that environmental contamination is largely separate from that of incoming raw materials and includes strains persisting, possibly for years, within the plant. Operational and sanitation procedures appear to have a significant impact on environmental contamination, with both plants having similar prevalence values for raw materials but disparate contamination prevalence values for the environmental sites. We also conclude that regular L. monocytogenes testing of drains, combined with molecular subtyping of the isolates obtained, allows for efficient monitoring of persistent L. monocytogenes contamination in a processing plant.

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Tracking of Listeria monocytogenes in Smoked Fish Processing Plants†

Journal of Food Protection ◽

10.4315/0362-028x-67.2.328 ◽

2004 ◽

Vol 67 (2) ◽

pp. 328-341 ◽

Cited By ~ 92

Author(s):

JOANNE THIMOTHE ◽

KENDRA KERR NIGHTINGALE ◽

KEN GALL ◽

VIRGINIA N. SCOTT ◽

MARTIN WIEDMANN

Keyword(s):

Listeria Monocytogenes ◽

Environmental Samples ◽

Control Strategies ◽

Fish Processing ◽

Smoked Fish ◽

Plant Environment ◽

Fish Samples ◽

Processing Plants ◽

Raw Fish ◽

Contact Surfaces

Four smoked fish processing plants were used as a model system to characterize Listeria monocytogenes contamination patterns in ready-to-eat food production environments. Each of the four plants was sampled monthly for approximately 1 year. At each sampling, four to six raw fish and four to six finished product samples were collected from corresponding lots. In addition, 12 to 14 environmental sponge samples were collected several hours after the start of production at sites selected as being likely contamination sources. A total of 234 raw fish, 233 finished products, and 553 environmental samples were tested. Presumptive Listeria spp. were isolated from 16.7% of the raw fish samples, 9.0% of the finished product samples, and 27.3% of the environmental samples. L. monocytogenes was isolated from 3.8% of the raw fish samples (0 to 10%, depending on the plant), 1.3% of the finished product samples (0 to 3.3%), and 12.8% of the environmental samples (0 to 29.8%). Among the environmental samples, L. monocytogenes was found in 23.7% of the samples taken from drains, 4.8% of the samples taken from food contact surfaces, 10.4% of the samples taken from employee contact surfaces (aprons, hands, and door handles), and 12.3% of the samples taken from other nonfood contact surfaces. Listeria spp. were isolated from environmental samples in each of the four plants, whereas L. monocytogenes was not found in any of the environmental samples from one plant. Overall, the L. monocytogenes prevalence in the plant environment showed a statistically significant (P < 0.0001) positive relationship with the prevalence of this organism in finished product samples. Automated EcoRI ribotyping differentiated 15 ribotypes among the 83 L. monocytogenes isolates. For each of the three plants with L. monocytogenes–positive environmental samples, one or two ribotypes seemed to persist in the plant environment during the study period. In one plant, a specific L. monocytogenes ribotype represented 44% of the L. monocytogenes–positive environmental samples and was also responsible for one of the two finished product positives found in this plant. In another plant, a specific L. monocytogenes ribotype persisted in the raw fish handling area. However, this ribotype was never isolated from the finished product area in this plant, indicating that this operation has achieved effective separation of raw and finished product areas. Molecular subtyping methods can help identify plant-specific L. monocytogenes contamination routes and thus provide the knowledge needed to implement improved L. monocytogenes control strategies.

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Molecular Typing To Trace Listeria monocytogenes Isolated from Cold-Smoked Fish to a Contamination Source in a Processing Plant

Journal of Food Protection ◽

10.4315/0362-028x-69.4.835 ◽

2006 ◽

Vol 69 (4) ◽

pp. 835-841 ◽

Cited By ~ 17

Author(s):

HIROMI NAKAMURA ◽

YUKA TOKUDA ◽

AYUMI SONO ◽

TOMOKA KOYAMA ◽

JUN OGASAWARA ◽

...

Keyword(s):

Listeria Monocytogenes ◽

Molecular Typing ◽

Pulsed Field Gel Electrophoresis ◽

Processing Plant ◽

Fish Processing ◽

Contamination Source ◽

Processing Equipment ◽

Smoked Fish ◽

Different Types ◽

Raw Fish

In this study, Listeria monocytogenes contamination in a cold-smoked fish processing plant in Osaka, Japan, was examined from 2002 to 2004. A total of 430 samples were collected and divided into five categories: raw fish, materials during processing, processing equipment, environment, and finished products. A total of 59 finished products were examined throughout this study. L. monocytogenes was isolated from four of these samples during summer and autumn but was not found during winter or spring. During the warmer seasons, L. monocytogenes was more prevalent on processing equipment, especially slicing machines (8 of 54 samples in summer and autumn versus 1 of 50 samples in winter and spring). L. monocytogenes was not detected on whole skins removed from 23 frozen raw fish. L. monocytogenes strains isolated from 56 samples were characterized by serotyping, pulsed-field gel electrophoresis, and three PCR-based methods. Seventy-seven L. monocytogenes strains were recognized as contaminants of the samples: 2 distinguishable strains were identified in each of 13 samples, 3 strains were identified in 2 samples, 5 strains were identified in 1 sample, and the other 40 strains were identified in 40 samples. Combining the results from these techniques, 77 strains were classified into 13 different types. Three of these types prevailed throughout the plant, and two of the three were also isolated from final products. The DNA subtype found in the product was also found on the slicing machines. Our findings suggest that the slicing machines at this plant were the source of the product contamination. Implementing an appropriate cleaning regime for the slicing machines was effective in preventing contamination.

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Molecular Studies on the Ecology of Listeria monocytogenes in the Smoked Fish Processing Industry

Applied and Environmental Microbiology ◽

10.1128/aem.67.1.198-205.2001 ◽

2001 ◽

Vol 67 (1) ◽

pp. 198-205 ◽

Cited By ~ 170

Author(s):

Dawn M. Norton ◽

Meghan A. McCamey ◽

Kenneth L. Gall ◽

Janet M. Scarlett ◽

Kathryn J. Boor ◽

...

Keyword(s):

Listeria Monocytogenes ◽

Food Processing ◽

Environmental Samples ◽

Raw Materials ◽

Raw Material ◽

Fish Processing ◽

Culture Methods ◽

Smoked Fish ◽

Molecular Approaches ◽

Automated Ribotyping

ABSTRACT We have applied molecular approaches, including PCR-based detection strategies and DNA fingerprinting methods, to study the ecology ofListeria 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 forL. 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 ≤ 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.

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Sources of Listeria monocytogenes Contamination in a Cold-Smoked Rainbow Trout Processing Plant Detected by Pulsed-Field Gel Electrophoresis Typing

Applied and Environmental Microbiology ◽

10.1128/aem.65.1.150-155.1999 ◽

1999 ◽

Vol 65 (1) ◽

pp. 150-155 ◽

Cited By ~ 203

Author(s):

Tiina Autio ◽

Sebastian Hielm ◽

Maria Miettinen ◽

Anna-Maija Sjöberg ◽

Kaarina Aarnisalo ◽

...

Keyword(s):

Rainbow Trout ◽

Listeria Monocytogenes ◽

Gel Electrophoresis ◽

Pulsed Field Gel Electrophoresis ◽

Hot Water ◽

Processing Plant ◽

Pulsed Field ◽

Eradication Program ◽

Fish Samples ◽

Raw Fish

ABSTRACT Sites of Listeria monocytogenes contamination in a cold-smoked rainbow trout (Oncorhynchus mykiss) processing plant were detected by sampling the production line, environment, and fish at different production stages. Two lots were monitored. The frequency of raw fish samples containing L. monocytogenes was low. During processing, the frequency of fish contaminated with L. monocytogenes clearly rose after brining, and the most contaminated sites of the processing plant were the brining and postbrining areas. A total of 303 isolates from the raw fish, product, and the environment were characterized by pulsed-field gel electrophoresis (PFGE). PFGE yielded nine pulsotypes, which formed four clusters. The predominating L. monocytogenespulsotypes of the final product were associated with brining and slicing, whereas contaminants of raw fish were not detected in the final product. Air-mediated contamination in the plant could not be proved. In accordance with these results, an L. monocytogenes eradication program was planned. The use of hot steam, hot air, and hot water seemed to be useful in eliminatingL. monocytogenes. None of the control samples taken in the 5 months after the eradication program was implemented containedL. monocytogenes.

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Characterization and Pathogenic Potential of Listeria monocytogenes Isolates from the Smoked Fish Industry

Applied and Environmental Microbiology ◽

10.1128/aem.67.2.646-653.2001 ◽

2001 ◽

Vol 67 (2) ◽

pp. 646-653 ◽

Cited By ~ 76

Author(s):

Dawn M. Norton ◽

Janet M. Scarlett ◽

Kelly Horton ◽

David Sue ◽

Joanne Thimothe ◽

...

Keyword(s):

Listeria Monocytogenes ◽

Mammalian Cells ◽

Raw Materials ◽

Plaque Assay ◽

Fish Processing ◽

Pathogenic Potential ◽

Genetic Lineages ◽

Smoked Fish ◽

Fish Industry

ABSTRACT This study was designed to evaluate the hypothesis that some of theListeria monocytogenes subtypes associated with foods, specifically smoked fish, may have an attenuated ability to cause human disease. We tested this hypothesis by using two different approaches: (i) comparison of molecular subtypes found among 117 isolates from smoked fish, raw materials, fish in process, and processing environments with subtypes found among a collection of 275 human clinical isolates and (ii) the evaluation of the cytopathogenicity of industrial isolates. Ribotyping and PCR-restriction fragment length polymorphism typing of the hlyA and actA genes differentiated 23 subtypes among the industrial isolates and allowed classification of the isolates into three genetic lineages. A significantly higher proportion of human isolates (69.1%) than industrial isolates (36.8%) were classified as lineage I, which contains human sporadic isolates and all epidemic isolates. All other industrial isolates (63.2%) were classified as lineage II, which contains only human sporadic isolates. Lineage I ribotypes DUP-1038B and DUP-1042B represented a significantly higher proportion of the human isolates than industrial isolates (5.1%). Lineage II ribotypes DUP-1039C, DUP-1042C, and DUP-1045, shown previously to persist in the smoked fish processing environment, represented nearly 50% of the industrial isolates, compared to 7.6% of the human isolates. Representatives of each subtype were evaluated with a tissue culture plaque assay. Lineage I isolates formed plaques that were significantly larger than those formed by lineage II isolates. Isolates from the smoked fish industry representing three ribotypes formed no plaques or small plaques, indicating that they had an impaired ability to infect mammalian cells. While L. monocytogenes clonal groups linked to human listeriosis cases and outbreaks were isolated, our data also suggest that at least some L. monocytogenes subtypes present in ready-to-eat foods may have limited human-pathogenic potential.

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One Group of Genetically Similar Listeria monocytogenes Strains Frequently Dominates and Persists in Several Fish Slaughter- and Smokehouses

Applied and Environmental Microbiology ◽

10.1128/aem.02288-05 ◽

2006 ◽

Vol 72 (6) ◽

pp. 4313-4322 ◽

Cited By ~ 109

Author(s):

Gitte Wulff ◽

Lone Gram ◽

Peter Ahrens ◽

Birte Fonnesbech Vogel

Keyword(s):

Listeria Monocytogenes ◽

Dna Analysis ◽

Random Amplified Polymorphic Dna ◽

Positive Sample ◽

Processing Plant ◽

Survey Period ◽

Smoked Fish ◽

Processing Plants ◽

Raw Fish ◽

Cleaning And Disinfection

ABSTRACT Contamination of foods with the human pathogen Listeria monocytogenes may occur during processing, and the purpose of this study was to determine whether genetically similar strains colonize different processing plants or whether specific persistent strains are unique to each processing plant. We hypothesized that specific L. monocytogenes strains may be better adapted to specific environmental niches in the processing environment. L. monocytogenes contamination patterns were identified by the collection of 686 and 267 samples from the processing environments: raw fish and products of four fish smokehouses and four fish slaughterhouses, respectively. Samples were collected both during production and after cleaning and disinfection. Typically, these samplings were separated by 1 to 3 months. Sampling sites were targeted toward areas likely to harbor the bacterium. L. monocytogenes was isolated from 213 samples, and one strain from each positive sample was typed by RAPD (random amplified polymorphic DNA) analysis with four different primers. The 213 strains were divided into 37 RAPD types. One RAPD type was predominant; 86 of 213 strains belonged to this type. This type was found in three smokehouses and two slaughterhouses and was predominant in three of these plants. A subset of 35 strains was also analyzed by amplified fragment length polymorphism typing, which confirmed the genetic similarity of the groups. Moreover, strains of the dominant RAPD type were indistinguishable from strains isolated frequently from smoked fish products 10 years ago. One smokehouse was surveyed for a year and a half, and the dominant RAPD type persisted throughout the survey period and accounted for 94 of 118 isolates. Our study indicates that strains of L. monocytogenes that are genetically very closely related may be especially adapted to colonizing the processing equipment or especially resistant to cleaning and disinfection.

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Raw and Processed Fish Show Identical Listeria monocytogenes Genotypes with Pulsed-Field Gel Electrophoresis

Journal of Food Protection ◽

10.4315/0362-028x-68.6.1228 ◽

2005 ◽

Vol 68 (6) ◽

pp. 1228-1231 ◽

Cited By ~ 22

Author(s):

ANNUKKA MARKKULA ◽

TIINA AUTIO ◽

JANNE LUNDÉN ◽

HANNU KORKEALA

Keyword(s):

Listeria Monocytogenes ◽

Gel Electrophoresis ◽

Pulsed Field Gel Electrophoresis ◽

Raw Material ◽

Processing Plant ◽

Pulsed Field ◽

Fish Samples ◽

Processing Plants ◽

Fish Product ◽

Raw Fish

A total of 257 raw fish samples at two different sites were examined for the presence of Listeria monocytogenes. The prevalence of L. monocytogenes was 4%. From 11 positive samples, nine different L. monocytogenes pulsed-field gel electrophoresis genotypes were recovered. From nine pulsotypes recovered from raw fish and 32 pulsotypes shown by 101 fish product isolates, two raw fish and fish product pulsotypes were indistinguishable from each other. Although the prevalence of L. monocytogenes in raw fish is low, the range of L. monocytogenes strains entering the processing plant in large amounts of raw material is wide. This indicates that the raw material is an important initial contamination source of L. monocytogenes in fish processing plants. This postulation is supported by the identical pulsotypes recovered from both raw and processed fish. Some L. monocytogenes strains entering a plant may thus contaminate and persist in the processing environment, causing recurrent contamination of the final products via processing machines.

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Evaluation of Surface Contamination and the Presence of Listeria monocytogenes in Fish Processing Factories

Journal of Food Protection ◽

10.4315/0362-028x-64.5.635 ◽

2001 ◽

Vol 64 (5) ◽

pp. 635-639 ◽

Cited By ~ 31

Author(s):

HANNA MIETTINEN ◽

KAARINA AARNISALO ◽

SATU SALO ◽

ANNA-MAIJA SJÖBERG

Keyword(s):

Listeria Monocytogenes ◽

Listeria Innocua ◽

Surface Contamination ◽

Fish Processing ◽

Monitoring Methods ◽

Salted Fish ◽

Smoked Fish ◽

Surface Samples ◽

Raw Fish ◽

Total Bacteria

The main objective of this study was to determine the level of surface contamination in fish processing factories and the presence of Listeria in the factory environment and products. Another objective was evaluation of the different hygiene-monitoring methods. Total aerobic heterotrophic and enterobacteria, yeast and mold samples were collected and ATP levels measured in 28 factories. The number of well or adequately washed and disinfected factories was small (2 of 28), in terms of total aerobic heterotrophic bacterial counts on the surfaces. Most surfaces contaminated with bacteria were heavily contaminated. Results of the ATP and the total bacteria contact agar slide methods were poorly correlated (r = 0.21) although 68% of the samples were categorized as good to moderate or unacceptable with both methods. The Listeria-positive surface samples usually contained increased numbers of total bacteria (70.9%). The contamination of products and raw fish together with Listeria spp. was 45% and with Listeria monocytogenes 12%. Cold smoked fish was the most contaminated, with 75% Listeria spp. and cold salted fish with 20% L. monocytogenes. Listeria innocua was found in the samples more than twice as often as L. monocytogenes.

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