Pig as a reservoir of CRISPR type TST4 <i>Salmonella enterica</i> serovar Typhimurium monophasic variant during 2009–2017 in China

CRISPR-based typing was performed to subtype isolates of <i>S.</i> Typhimurium and its monophasic variant <i>Salmonella</i> 4,[5],12:i:- from humans and animals between 2009 and 2017 in China. CRISPR typing classified all isolates into two lineages and four sub-lineages. All isolates from Lineage II and Lineage IB-1 were <i>Salmonella</i> Typhimurium. All of <i>Salmonella</i> 4,[5],12:i: – isolates were distributed in Lineage IA and Lineage IB-2, which all belonged to ST34 by MLST typing. Only Lineage IB-2 contained ST34 isolates from both <i>Salmonella</i> Typhimurium and <i>Salmonella</i> 4,[5],12:i:-. Among the isolates of ST34, TST4 was identified as the most common CRISPR type representing 86.5% of <i>Salmonella</i> 4,[5],12:i:- and 14.5 % of <i>Salmonella</i> Typhimurium mainly from pigs and humans. This study demonstrated that TST4-ST34 isolates were predominant in <i>Salmonella</i> 4,[5],12:i:-, and pig was the main reservoir for <i>Salmonella</i> 4,[5],12:i:- in China, which might have the potential to transmit to humans by pig production.本研究采用基于CRISPR的分型（CRISPR-based typing）技术，对2009年至2017年间中国境内分离自人类与动物的鼠伤寒沙门氏菌（Salmonella Typhimurium）及其单相变种沙门氏菌4,[5],12:i:-（Salmonella 4,[5],12:i:-）的分离株进行亚型分型。CRISPR分型将所有分离株划分为2个进化谱系与4个亚谱系。谱系II与谱系IB-1的全部分离株均为鼠伤寒沙门氏菌。所有沙门氏菌4,[5],12:i:-分离株均分布于谱系IA与谱系IB-2中，经多位点序列分型（Multilocus Sequence Typing，MLST）鉴定，该两类亚谱系内的分离株均属于ST34型。仅谱系IB-2同时包含源自鼠伤寒沙门氏菌与沙门氏菌4,[5],12:i:-的ST34型分离株。在ST34型分离株中，TST4型为最常见的CRISPR分型类型，分别占沙门氏菌4,[5],12:i:-分离株的86.5%与鼠伤寒沙门氏菌分离株的14.5%，其分离来源主要为猪与人类。本研究证实，TST4-ST34型分离株在沙门氏菌4,[5],12:i:-中占据主导地位；猪是中国境内沙门氏菌4,[5],12:i:-的主要宿主储存库，该菌株具备通过生猪养殖环节向人类传播的潜在风险。