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Background Food is the main source of Listeria monocytogenes (Lm) infection. Lm is a highly heterogeneous species composed of hypervirulent and hypovirulent clones. Understanding the distribution of Lm clonal complexes (CCs) in different food categories has strong implications for risk assessment. The aim of this work was to analyse collection of Lm strains of National Reference Laboratory (NRL Lm) in order to assess link between genetic profile and matrices and the level of pathogenicity of circulating strains based on CCs. Methods NRL Lm database actually consists of 906 sequenced strains isolated in 10 years from 5 food compartments (meat, fish, dairy, vegetables and composite dishes). Epidata were analysed to remove redundant strains based on the same epidemiological description. After that, WGS data from 465 Lm strains were investigated. In silico MLST was defined and Roary 3.12.0 was used to obtain a pan-genome profile. Genes were later uploaded to Pasteur Institute platform for characterization. Results In silico MLST identified 36 CCs and 6 singleton. CC9 (23.0%), CC8 (15.3%) and CC121 (13.3%) were the prevalent CCs. In particular, CC9 was present in 35.2% of meat samples and CC8 in 25.8% of fish samples. Pan genome profile revealed high prevalence (&amp;gt;98%) of genes related to biofilm formation and resistance to environmental stress in CC9 strains and genes involved in tolerance to quaternary ammonium compounds in CC121 strains. Conclusions Results, in particular for meat products, confirmed in Italy, the prevalence of hypovirulent Lm strains previously observed at European Union level. The high presence of stress resistance and disinfectant tolerance genes in these strains could make them able to persist in food-production environment and should be taken into account evaluating the health hazards. In fish product is also relevant the prevalence of CC8 strains which are potentially highly pathogenic and have been responsible of recent European multi country outbreak. Key messages Pangenome of Listeria monocytogenes isolated from Italian food revealed high presence of disinfectant tolerance and stress resistance genes in meat products and virulence genes in fish products. Listeria monocytogenes CC9 and CC121 prevalence in Italian meat product confirms occurrence of hypovirulent strains detected at European Union level.

Listeria monocytogenes clones in Italian food products: virulence and environmental adaptation