Integrated Genomic and Epidemiological Analysis of Listeria monocytogenes Isolates from Food, Environmental, and Clinical Sources in Yantai, China

Methods From 2014 to 2024, a total of 2,150 samples were collected from food safety risk surveillance, including foods, environments, and clinical infection cases in Yantai. A total of 45 isolates were used for phylogenetic analysis, and 21 of them isolated in local area. The drug sensitivity test was conducted using the microbroth dilution method for 9 different antibiotics. Results The overall detection rate of Lm was 1.77% (38/2,150), with edible fungi showing the highest contamination rate at 20% (8/40). Phylogenetic analysis revealed that all isolates clustered closely with the reference strain NCTC10357. All isolates carried five antibiotic resistance genes (fosX, lin, mprF, sul and norB), with lin, mprF, and norB universally detected. Clindamycin showed low susceptibility, where only 19% (4/21) of strains were susceptible and 80.9% (17/21) exhibited intermediate resistance. Except for sulfamethoxazole - trimethoprim, one of them showed full resistance. A total of 83 virulence genes encoding 44 factors were identified, but exotoxin-related genes (e.g., llsD、llsY) exhibited a high loss rate of 76.2% (16/21), suggesting adaptation to environmental niches. The predominant serotype was 1/2a (52.4%, 11/21), and the three major sequence types, ST121, ST3, and ST8, each accounted for 23.8% (5/21), indicating clonal expansion. Environmental isolates were distributed across all phylogenetic branches and overlapped with clinical strains. Comparative genomics showed that Yantai strains shared ≥ 93.5% average nucleotide identity (ANI) with European and South American isolates, highlighting transcontinental genetic relatedness. Conclusions Lm contamination in Yantai poses significant public health risks, driven by clonal strains with broad environmental persistence and partial virulence attenuation. The high prevalence in edible fungi and cold-chain products emphasizes the urgent need for targeted surveillance. This study provides the first comprehensive genomic-epidemiological profile of Lm in Yantai, demonstrating its genetic connectivity to global lineages and informing evidence-based interventions to mitigate foodborne listeriosis.