Listeria innocua and Salmonella panama in mussels: a comparative study.

Bivalve molluscs are exposed to a wide range of contamination by pathogenic bacteria and viruses. Therefore, the behavior of bacterial pathogens in bivalves after harvesting is important in terms of food safety. Mussels were artificially contaminated with Listeria innocua and Salmonella panama, held under different conditions, and then examined for Listeria and Salmonella viable counts. In a simplified depuration system, L. innocua levels were lower than those observed for S. panama in mussels during the same period and under the same conditions. This result may be related to the rapid die-off reported for Listeria in seawater. In mussels stored in air, the two pathogens presented similar behaviors: levels of both pathogens remained constant in mussels during the storage period in air. However, in shucked mussels Listeria innocua counts increased with the duration of storage, whereas Salmonella panama showed a slight decrease.

Incidence of Listeria spp. in Breton live shellfish.

Live shellfish samples (120) were collected from nine littoral sites in Brittany (western France). They were screened for Listeria spp. and a count of faecal coliforms was carried out. Analysis of the results revealed Listeria spp. in 55% of samples, a much higher rate than the previous, infrequent, recorded data. Furthermore, the study demonstrated that the frequency of Listeria spp. in winter was more important than in summer (P < 0.001), and underlined a significant relationship between the occurrence of these bacteria and the concentration of faecal coliforms (P < 0.001). Finally, comparison of the official and Gen-Probe methods revealed the limits of the standardized technique in the search for L. monocytogenes in shellfish.