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

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.

Efficient subtyping of Yersinia enterocolitica bioserotype 4/O:3 with pulsed-field gel electrophoresis

“…The cells were harvested from 2 ml of TSB after overnight enrichment at room temperature. DNA isolation was performed according to Autio et al (1999) omitting mutanolysin from the lysis buffer. In this method, the plugs were lysed for only 3 h and a single 2-h wash with ESP was used.…”

THE INCIDENCE AND LEVEL OF LISTERIA SPP. AND LISTERIA MONOCYTOGENES CONTAMINATION IN PROCESSED POULTRY AT A POULTRY PROCESSING PLANT

“…This colonization, as well as job rotation of staff among departments, have been identified as primary mechanisms for contamination of the final products in some processing lines. In most cases, the contamination of the final product is believed to have occurred during processing because the strains found in the incoming raw materials are different from the strains found in the final product (Autio et al 1999;Fonnesbech Vogel et al 2001a,b). In other cases, when the strains of L. monocytogenes contaminating the raw materials were indistinguishable from those isolated from the final product, the contaminated incoming raw materials are considered to be the source of continuing contamination (Lawrence and Gilmour 1995;Giovannacci et al 1999;Fonnesbech Vogel et al 2001a).…”

Gravad (Gravlax) and cold‐smoked salmon, still a potential source of listeriosis

“…L. monocytogenes isolated from cold-smoked fish of manufacturer A harboured two serovars (1/2a and 4b), each with unique Asc I profiles, implying that serotyping and genotyping of several isolates from each food sample is important (Loncarevic et al 1996;Ericsson et al 1997;Autio et al 1999;Dauphin et al 2001). Furthermore, products from the same manufacturer (A) purchased in both Germany and Sweden contained L. monocytogenes strains with the same Asc I and Apa I profiles, indicating a common source of contamination, which could be the raw fish, employees or the environment in the processing plant.…”