Prevalence and serotyping of Listeria monocytogenes in Portuguese live bivalve molluscs sampled in various steps along the sanitary control process

摘要

The prevalence and contamination levels of Listeriamonocytogenes were investigated in live bivalve molluscsfor human consumption, collected in varioussteps of the commercial and sanitary circuits in theNorth of Portugal. Samples of di¡erent species werecollected per lot before and after depuration treatmentin two depuration units and further, whenplaced in retail markets. Listeria monocytogenes wasisolated from 4% of the samples although with verylow contamination levels (less than 100MPNg 1).None of the environmental (non-depurated) sampleswere contaminated with the food-borne pathogen.The positive samples involved depurated and commercializedsamples from two lots, one in each circuit.Two serotypes (1/2a and 3b) were detectedamong the isolated strains. This study demonstratedthe possibility of occurrence of L.monocytogenes contaminationof live bivalvemolluscs along the sanitarycontrol circuit, including at the retailmarket level. AsL. monocytogenes grows well at refrigerated temperaturesand in high salt matrixes such as seafood itspresence in these products should not be overlooked.