[Genomic characteristics and antimicrobial resistance of Listeria monocytogenes isolated from food in Beijing, City 2022].

Objective: To analyze the genomic characteristics and antibiotic resistance of Listeria monocytogenes isolated from food sources in Beijing City in 2022. Methods: A total of 83 strains of Listeria monocytogenes were isolated from three major categories of food, namely raw poultry, raw livestock meat and ready-to-eat foods, in Beijing's food safety risk monitoring in 2022. Whole-genome sequencing (WGS) was performed to determine serogroups, multilocus sequence typing (ST) and core genome multilocus sequence typing (cgMLST). Virulence genes and antibiotic resistance genes were identified using the VFDB and ResFinder 3.0 databases. Antimicrobial susceptibility to eight antibiotics was tested via the broth microdilution method. Results: The predominant serogroup was 1/2a, 3a (61.2%). All the isolates were divided into 14 STs, with ST121 (21.7%), ST8 (20.5%), ST9 (13.3%), and ST87 (13.3%) as the dominant types. All 83 isolates were classified into 75 cgMLST types, with six clusters showing identical profiles, indicating potential clonal transmission. Comparative genomic analysis revealed that strains of the same ST clustered together regardless of geographic origin, and some Beijing isolates differed by fewer than 10 alleles from strains isolated in other countries. All the isolates in the study carried virulence islands 1(LIPI-1) and LIPI-2. LIPI-3 was detected in ST1, ST11 and ST3 isolates, while LIPI-4 was found in ST87 isolates. About 42 isolates (50.6%, including ST1, ST11, ST5, ST307, ST8, ST9, ST155, and ST3) harbored SSI-1, and 18 ST121 isolates carried SSI-2. Only 3.61% (three strains) and 4.82% (four strains) of isolates exhibited resistance to tetracycline and erythromycin, respectively. No resistance to other tested antibiotics was observed. Conclusion: Foodborne Listeria monocytogenes in Beijing exhibits high genomic diversity but is dominated by specific STs, some of which are associated with hypervirulence. Some Beijing isolates have homology with food-derived isolates from other countries.