Objective: To analyze the molecular characteristics of Listeria monocytogenes strains from ready-to eat food in China. Methods: A total of 239 Listeria monocytogenes strains isolated from ready-to-eat food in 2017, all strains underwent whole-genome sequencing (WGS) , and comparisons uncovered population structure derived from lineages, clonal complex, serogroups, antimicrobial susceptibility and virulence, which were inferred in silico from the WGS data. Core genome multilocus sequence typing was used to subtype isolates. Results: All strains were categorized into three different lineages, lineage Ⅱ was the predominant types in food, and IIa was the main serogroups. CC8, CC101 and CC87 were the first three prevalent CCs among 23 detected CCs, accounting for 49.4%. Only 4.6% (11 isolates) of tested strains harbored antibiotic resistance genes, which were mostly trimethoprim genes (7 isolates, 2.9%). All strains were positive for LIPI-1, and only a part of strains harbored LIPI-3 and LIPI-4, accounting for 13.8% (33 isolates) and 14.2% (34 isolates), respectively. ST619 carried both LIPI-3 and LIPI-4. 51.5% (123 isolates) of strains carried SSI-1, and all CC121 strains harbored SSI-2. Different lineages, serogroups and CCs can be separated obviously through cgMLST analysis, and 24 sublineages were highly concordant with CCs. Conclusion: Ⅱa was the main serogroups in ready-to-eat food isolates in China; CC8, CC101 and CC87 were the prevalent CCs, and CC87 isolates was hypervirulent isolates, cgMLST method can be adopted for prospective foodborne disease surveillance and outbreaks detection.
目的： 分析我国即食食品中单核细胞增生李斯特菌的分子流行病学特征。 方法： 将2017年食品安全风险监测即食食品中分离的单核细胞增生李斯特菌作为研究菌株，共239株，分离自27个省份。对菌株进行全基因组测序，分析其谱系、克隆群（CC）、序列分型（ST）和血清群；通过VFDB和BIGSdb-Lm数据库获得其毒力基因分布；采用微量肉汤稀释法检测菌株对8种抗生素的敏感性；采用核心基因组多位点序列分型方法（cgMLST）进行分子分型。 结果： 实验菌株分属在3个谱系，以谱系Ⅱ为主，共155株（64.9%）；血清群以Ⅱa为主，共133株（55.6%）；分为23个CC型，以及1个未分CC型的ST619，其中CC8、CC101和CC87为优势CC型，共占49.4%（118株）；仅4.6%（11株）的菌株携带耐药基因，主要为甲氧苄啶耐药基因（7株，2.9%）。所有菌株均携带单核细胞增生李斯特菌毒力岛（LIPI）1，携带LIPI-3和LIPI-4的菌株分别占13.8%（33株）和14.2%（34株），ST619同时携带LIPI-3和LIPI-4。51.5%（123株）的菌株携带应激生存岛（SSI）1，10株CC121菌株均携带SSI-2。核心基因组多位点序列分型方法能将不同谱系、血清群和CC型的菌株明显分开，共分为24个亚群，与CC型基本保持一致。 结论： 我国即食食品中菌株以Ⅱa型血清群为主，CC8、CC101和CC87为优势CC型，其中，CC87为流行性高毒菌株。基于全基因组测序的分型方法cgMLST分辨力高，可用于我国食源性疾病的监测和暴发识别。.
Keywords: Core genome multilocus sequence typing; Genome-wide sequencing; Listeria monocytogenes; Molecular epidemiology; Ready-to-eat food.