Occurrence and persistence of Listeria spp. in the environment of ewe and cow's milk cheese dairies in Portugal unveiled by an integrated analysis of identification, typing and spatial–temporal mapping along production cycle

Eight dairies, located in two distant geographic regions of Portugal, were screened along the production cycle in order to evaluate the presence and distribution of Listeria spp. in their environment. Three dairies in each region were positive for the presence of listeriae and 213 isolates were obtained. Based on an integrated analysis of RAPD fingerprints with three primers, molecular identification and genomic typing of isolates was performed followed by spatial and temporal mapping on dairy plants.The occurrence of Listeria species by region was noticeable different. Listeria monocytogenes prevailed in South Portugal dairies and L. innocua presented the highest occurrence in Azores, whereas L. seeligeri and L. ivanovii were detected in distinct regions. Dairies were at risk of contamination, from more than one source, whatever the stage in the production cycle and the surface materials used. For the three prevalent species, most of the genomic types were dairy and sampling time specific. Nonetheless, more than one type could be found in each dairy at a particular site and, in a few cases, even for different species. Some dairies also shared types, mainly for L. innocua and usually at the same stage of the production cycle.For L. monocytogenes, PCR serotyping was applied and 52% of genomic types were serotype 4b. An equal frequency of genomic types (24%) was found for serotypes 1/2b or 3b and 1/2a or 3a. The global pattern of types within a dairy is not constant, suggesting cycles of elimination and recontamination along the production cycle.