Tracking of Listeria monocytogenes in Smoked Fish Processing Plants

Abstract

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.

Construction and Analysis of Fractional Multifactorial Designs To Study Attachment Strength and Transfer of Listeria monocytogenes from Pure or Mixed Biofilms after Contact with a Solid Model Food

“…However, cleaning and disinfection operations may be effective only against the immediate risk. Yet incidents where L. monocytogenes cells remain on surfaces, despite multiple cleaning and disinfection procedures, have been frequently reported (15,47); such L. monocytogenes strains are called persistent. It is of some importance to remember that the aging of biofilms, since it causes an increased resistance to disinfectants (10), is likely to be a factor in contributing to persistence.…”

Molecular Ecology of Listeria monocytogenes : Evidence for a Reservoir in Milking Equipment on a Dairy Farm

“…Floors and floor drains, areas previously described as sources of L. monocytogenes in food plant environments (34), were also included. Samples were collected using a Bacti-Sponge kit (Hardy Diagnostics, Santa Maria, CA) moistened with 10 ml of neutralizing buffer (Difco; BD Diagnostics, Sparks, MD) (19,33). For the milking equipment, a sponge was used to wipe the inner surface of the selected site.…”

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

“…Molecular subtyping of strains from raw fish, processing environments, and packed products has suggested that contamination during processing rather than contamination directly from raw fish is the principal cause of product contamination (1,9,23,24). The production process for cold-smoked salmon and other coldsmoked fish does not include a listeriacidal step, and only a better understanding of the sources and contamination routes of L. monocytogenes can specifically reduce the contamination of the product.…”