Abstract
Salmonella enterica (S. enterica) is an important foodborne pathogen, causing food poisoning and human infection, and critically threatening food safety and public health. Salmonella typing is essential for bacterial identification, tracing, epidemiological investigation, and monitoring. Serotyping and multilocus sequence typing (MLST) analysis are standard bacterial typing methods despite the low resolution. Core genome MLST (cgMLST) is a high-resolution molecular typing method based on whole genomic sequencing for accurate bacterial tracing. We investigated 250 S. enterica isolates from poultry, livestock, food, and human sources in nine provinces of China from 2004 to 2019 using serotyping, MLST, and cgMLST analysis. All S. enterica isolates were divided into 36 serovars using slide agglutination. The major serovars in order were Enteritidis (31 isolates), Typhimurium (29 isolates), Mbandaka (23 isolates), and Indiana (22 isolates). All strains were assigned into 43 sequence types (STs) by MLST. Among them, ST11 (31 isolates) was the primary ST. Besides this, a novel ST, ST8016, was identified, and it was different from ST40 by position 317 C → T in dnaN. Furthermore, these 250 isolates were grouped into 185 cgMLST sequence types (cgSTs) by cgMLST. The major cgST was cgST235530 (11 isolates), and only three cgSTs contained isolates from human and other sources, indicating a possibility of cross-species infection. Phylogenetic analysis indicated that most of the same serovar strains were putatively homologous except Saintpaul and Derby due to their multilineage characteristics. In addition, serovar I 4,[5],12:i:- and Typhimurium isolates have similar genomic relatedness on the phylogenetic tree. In conclusion, we sorted out the phenotyping and genotyping diversity of S. enterica isolates in China during 2004–2019 and clarified the temporal and spatial distribution characteristics of Salmonella from different hosts in China in the recent 16 years. These results greatly supplement Salmonella strain resources, genetic information, and traceability typing data; facilitate the typing, traceability, identification, and genetic evolution analysis of Salmonella; and therefore, improve the level of analysis, monitoring, and controlling of foodborne microorganisms in China.
Highlights
Salmonella enterica (S. enterica) is one of the primary foodborne pathogens to cause food poisoning and human infection (Zhang et al, 2015)
We examine the serotypes, multilocus sequence typing (MLST), and Core genome MLST (cgMLST) of S. enterica isolates from different sources in nine provinces in China from 2004 to 2019 to investigate their phenotyping and genotyping diversities and genetic relationships
We serotyped 250 Salmonella isolates from different sources in China in the past 16 years, and the results show all strains tested in the study were divided into 36 serotypes, and Salmonella serovars Enteritidis and Typhimurium were still the major serovars, which is similar to a recent report (Perry et al, 2020; Shen et al, 2020)
Summary
Salmonella enterica (S. enterica) is one of the primary foodborne pathogens to cause food poisoning and human infection (Zhang et al, 2015). Foodborne salmonellosis is an important public health concern worldwide, and it annually causes about 115 million infections and 370,000 deaths globally (Seif et al, 2018). The primary sources of S. enterica foodborne infection include poultry eggs, meats, and their derived products (Arthur et al, 2008). It is crucial to monitor Salmonella from animal food, especially poultry eggs, and their derived food products (Mezal et al, 2014). Accurate typing and tracing are essential for microbial epidemiological investigation, food safety, and public health. Bacterial typing methods include phenotyping and genotyping. Among them, serotyping and multilocus sequence typing (MLST) are the most frequently used
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