Genetic characterization of Listeria monocytogenes strains from the Seeliger’s historical “special Listeria culture collection” (1918–1986)

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Introduction Listeria monocytogenes ( L. monocytogenes ) is a widespread foodborne pathogen that continues to pose a major challenge to public health and the food industry. Methods To explore the genomic diversity of historical isolates, we used whole genome sequencing (WGS) both short- and long-read technologies to obtain high quality genomes of 64 historical L. monocytogenes isolates collected between 1918 and 1986. These isolates originated from environmental, animal, and human sources obtained from the collection from Professor Seeliger. Results The isolates displayed a substantial genetic diversity, representing 15 clonal complexes (CCs), 40 sequence types (STs) and 59 core genome multilocus sequence types (cgMLST). The most frequently identified STs were ST2 ( n = 8), ST7 ( n = 6) and ST9 ( n = 4). All isolates harbored known virulence genes, while 35 isolates contained mobile genetic elements (MGEs), ranging from 1 to 11 per isolate. Ten isolates also carried a plasmid. Every isolate possessed the intrinsic resistance genes fosX and lin , and none carried acquired antimicrobial resistance genes (ARGs). Accessory genome diversity mainly followed phylogenetic positioning, and rendered limited within, but not between lineage variability. Discussion/conclusion WGS revealed high genetic diversity among the Seeliger L. monocytogenes isolates. Their close relatedness to contemporary isolates underscores the strong adaptability across sources and time, emphasizing the need for better prevention strategies.