Sammendrag
To investigate the diversity, distribution, persistence, and prevalence
of stress survival and resistance genes of Listeria monocytogenes clones dominating
in food processing environments in Norway, genome sequences from 769 L. monocytogenes isolates from food industry environments, foods, and raw materials (512
of which were sequenced in the present study) were subjected to whole-genome
multilocus sequence typing (wgMLST), single-nucleotide polymorphism (SNP), and
comparative genomic analyses. The data set comprised isolates from nine meat
and six salmon processing facilities in Norway collected over a period of three decades. The most prevalent clonal complex (CC) was CC121, found in 10 factories, followed by CC7, CC8, and CC9, found in 7 factories each. Overall, 72% of the isolates
were classified as persistent, showing 20 or fewer wgMLST allelic differences toward an isolate found in the same factory in a different calendar year. Moreover,
over half of the isolates (56%) showed this level of genetic similarity toward an isolate collected from a different food processing facility. These were designated as
pervasive strains, defined as clusters with the same level of genetic similarity as persistent strains but isolated from different factories. The prevalence of genetic determinants
associated with increased survival in food processing environments, including heavy
metal and biocide resistance determinants, stress response genes, and inlA truncation
mutations, showed a highly significant increase among pervasive isolates but not
among persistent isolates. Furthermore, these genes were significantly more prevalent
among the isolates from food processing environments compared to in isolates from
natural and rural environments (n = 218) and clinical isolates (n = 111) from Norway
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