Daily Variability of Listeria Contamination Patterns in a Cold-Smoked Salmon Processing Operation

Abstract

An understanding of Listeria transmission and contamination patterns in processing environments of ready-to-eat foods is critical for improving control of Listeria monocytogenes. A cold-smoked fish processing operation was the site used to study variability in Listeria contamination in a processing environment associated with a ready-to-eat food product throughout one production week (five consecutive days). Intensive testing was conducted on finished products and environmental samples collected at the beginning, middle, and end of each working day. A total of 20 finished products and 22 to 36 environmental samples were collected at each sampling time, and an additional 12 environmental samples were collected on days 4 and 5. Overall, a total of 782 samples, 300 finished products and 482 environmental samples, were tested. All samples were collected from processing steps after smoking, including skinning, trimming, slicing, staging, and packing. A total of 28 finished and 57 environmental samples (9.3 and 11.8%, respectively) were positive for Listeria spp. (including 1 and 5 samples positive for L. monocytogenes, respectively). DNA sequencing of the sigB gene allowed differentiation of eight Listeria subtypes. Listeria prevalence varied significantly between days, and a high prevalence in both environmental samples and finished products on day 3 was likely associated with a point source contamination event by a single Listeria welshimeri subtype. There were no consistent differences in Listeria prevalence among samples collected from the beginning, middle, and end of the production day, but subtype data often revealed unique contamination patterns for samples collected at different times of a given day. Listeria contamination patterns and prevalences were highly variable between days and within a given day. These findings indicate that chance events play an important role in the contamination of finished products, thus complicating efforts to define Listeria transmission patterns in processing environments associated with ready-to-eat foods.

Incidence of Listeria monocytogenes and Listeria spp. in a Small-Scale Mushroom Production Facility

“…However, approximately equal proportions of the two species were found in separate fish processing plants by Eklund et al (27) and Chen et al (15). Conversely, Hu et al (34) did not recover any L. innocua from 782 environmental and product samples taken from a cold-smoked fish processing facility. Further studies are needed to determine if the reported variation in proportions of L. monocytogenes to L. innocua is related to differential growth during the enrichment procedure or if nonpathogenic species of Listeria might affect growth and survival of L. monocytogenes in agricultural and food processing environments.…”

Positive Correlation Between the Expression of inlA and inlB Genes of Listeria monocytogenes and Its Attachment Strength on Glass Surface

“…3 L. monocytogenes is ubiquitous in nature; thus, it is commonly isolated from farms and food processing facilities. [5][6][7][8][9][10] Since L. monocytogenes has the ability to grow and persist at refrigeration temperatures, 11,12 even a small quantity of the bacteria is a potential food safety concern. The L. monocytogenes that is attached to food processing surfaces is one source of the Listerial contamination in processed food products, especially ready-to-eat foods such as cheese, meat, and poultry.…”

Listeria monocytogenesin Multiple Habitats and Host Populations: Review of Available Data for Mathematical Modeling

“…Thus contamination of RTE foods in processing plants is likely to be a stronger risk factor for human exposure than contamination closer to consumption (e.g., in household kitchens). Consequently, understanding and reducing contamination in food processing plant environments has been a focus for many years (Cox et al, 1989;Hu et al, 2006;Samelis and Metaxopoulos, 1999), while contamination in retail environments has only been addressed more recently (Sauders et al, 2004).…”