一起食源性疾病暴发事件分离的2种血清型沙门菌的病原学分析

目的 对一起食源性疾病暴发事件中分离的2种血清型沙门菌进行病原学分析。方法 采集2022年9月8日某学校暴发事件中病例肛拭子11件、可疑污染食品13件和环境样本10件；对病例肛拭子分别使用亚硒酸盐煌绿增菌液和脑心浸液肉汤（BHI）进行增菌培养，在完成常见肠道病原菌荧光PCR检测后，根据结果开展相应致病菌的分离培养；对可疑污染食品参照食品安全国家标准进行检测；每份肛拭子样本和食品样本均挑取多个疑似沙门菌菌落进行血清学凝集和全基因组测序；根据全基因组测序结果确定沙门菌血清型，基于菌株核心基因组单核苷酸多态性（SNP）进行聚类分析。结果 病例肛拭子和可疑污染食品沙门菌检出率分别为9/11和5/13，其中4例病例肛拭子和4件可疑污染食品样本均分离到2种血清型沙门菌（乌干达沙门菌和伊迪坎沙门菌），其余阳性样本分离沙门菌均为单一乌干达沙门菌血清型或单一伊迪坎沙门菌血清型。11件病例肛拭子样本接种BHI增菌液后12 h和24 h沙门菌荧光PCR检出率均为9/11，与分离培养结果一致。2种血清型沙门菌在基于核心基因组SNP构建的聚类树中形成2个相互独立且遗传距离较远的分支，而每一种血清型沙门菌也表现出基因组多态性，乌干达沙门菌之间SNP差异个数介于0~14个，伊迪坎沙门菌之间SNP差异个数介于0~23个。结论 本次事件为乌干达沙门菌和伊迪坎沙门菌共同导致食源性疾病暴发事件，基于BHI对病例肛拭子增菌并进行沙门菌荧光PCR检测的方案可在暴发中应用。

Etiological analysis on a foodborne disease outbreak caused by two serotypes of Salmonella

Objective To understand the etiological characteristics of 2 serotypes of Salmonella strains isolated from a foodborne disease outbreak. Methods A total of 11 anal swabs of the cases, 13 suspected contaminated food and 10 environmental samples were collected from a foodborne disease outbreak occurred on September 8, 2022 in a school. The anal swabs were enriched with selenite brilliant green enrichment broth (SBG) and brain heart infusion broth (BHI) respectively. PCR detection and culture of common intestinal pathogens were carried out. The suspected food samples were tested according to national standards for food safety. Multiple suspected Salmonella colonies were obtained and selected for serotype determination and whole genome sequencing. Serotypes were determined based on the whole-genome sequence, and clustering analysis was performed based on core genome single nucleotide polymorphism (SNP). Results The positive rates of Salmonella in anal swabs and suspected food samples were 9/11 and 5/13 respectively. Both Salmonella Uganda and Salmonella Idikan were isolated from 4 anal swabs and 4 suspected food samples. For the remaining samples, only Salmonella Uganda or Salmonella Idikan was isolated in each sample. The positive rate of Salmonella in 11 anal swabs of the cases after BHI enrichment for 12 h and 24 h were all 9/11 in real-time PCR, same to the culture results. Salmonella Uganda and Salmonella Idikan formed two independent and genetically distant lineages in the clustering tree based on core genome SNP, and 0-14 and 0-23 SNP were observed in Salmonella Uganda and Salmonella Idikan respectively. Conclusions This foodborne disease outbreak was probably caused by Salmonella Uganda and Salmonella Idikan, which both exhibited strong genetic diversity. The PCR based pathogen screening strategy plus pathogen enrichment for cases'' annal swabs can be used in the routine outbreak investigation.