重庆市某高校一起鼠伤寒沙门菌引起的食源性疾病暴发事件溯源调查和病原分析

Tracing and pathogen-analyzing of a foodborne disease outbreak of Salmonella typhimurium in a university in Chongqing City by whole-genome sequencing

目的对重庆市某高校一起鼠伤寒沙门菌引起的食源性疾病暴发事件进行实验室病原学分析。方法按照食品安全国家标准(GB 4789.4—2016)对11株沙门菌分离株进行生化和血清型鉴定;使用微量肉汤稀释法进行药敏测试;采用脉冲场凝胶电泳(PFGE)和全基因测序(WGS)进行分子分型、毒力和耐药基因分析。结果11株沙门菌全部为鼠伤寒沙门菌;在测试的15种抗生素中,所有菌株仅对四环素耐药;所有菌株的PFGE带型一致;WGS鉴定与血清学表型实验结果一致,所有菌株均携带2个四环素类耐药基因和10个毒力岛;溯源分析结果显示所有菌株的ST型相同,wgSNP进化树显示所有菌株可聚为一簇。结论11株鼠伤寒沙门菌序列高度同源,说明患者、环境和食品分离株来源相同,结合流行病学调查结果判定此次食源性疾病暴发事件是由食品加工人员使用器皿生熟不分引起食品污染所致。

Objective Laboratory pathogenic analysis of Salmonella that caused a foodborne outbreak in a university in Chongqing were carried out.Methods Biochemical characterization and serotyping of 11 strains of Salmonella were carried out based on national standard method(GB 4789.4—2016);antibiotics sensitivity testingwere tested by microbroth dilution method;the molecular typing,virulence and drug resistance genes were analyzed by pulsed-Field gel electrophoresis(PFGE)and whole genome sequencing(WGS).Results A total of 11 strains of Salmonella were Salmonella typhimurium;among the 15 antibiotics tested,all strains were only resistant to tetracycline;The PFGE bands of all strains are consistent;WGS identification is consistent with the results of serological phenotype experiments,and all strains carry 2 tetracycline resistance genes and 10 virulence islands;The traceability analysis results showed that all strains had the same ST type,and the wgSNP evolutionary tree showed that all strains could cluster together in same branch.Conclusion The 11 strains of Salmonella typhimurium have highly homologous sequences,indicating that the source of the patient,environment,and food isolates are the same.Based on epidemiological investigation results,it is determined that the outbreak of foodborne diseases was caused by food contamination caused by food processors not distinguishing between raw and cooked food when using utensils.