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Background: Salmonella enterica subsp. enterica serovar Typhimurium (antigenic formula 1,4,[5],12:i:1,2) is a widely distributed serovar, representing the second most common serovar in the United States and the European Union. This serovar belongs to the serogroup serovar of the O:4 (B) , there is one serogroup. One variant named S. Salmonella Typhimurium var. Copenhagen, which lacks the factor 5 in the O antigen (1,4,12:i:1,2). This The serotype 1,4,[5],12:i:–, which lacks the second-phase H2 flagellar antigen, is a monophasic variant of Salmonella Typhimurium. This serovar was named Typhimurium because it produces "produces Typhi like symptoms in the murine (mouse) model. In humans, it is frequently associated with acute gastroenteritis. S. Typhimurium has been used as model to understand the pathogenicity of Salmonella. Salmonella Typhimurium is the most extensively studied serovar for nontyphoidal salmonellosis and has emerged as the primary model for nontyphoidal Salmonella research. The S.  Serovar Typhimurium can cause disease in a wide range of hosts and invasive strains have been reported in some African countries. This Typhimurium LT2 strain has been particularly well-characterized and remains widely used in research since the 1940s. Both Salmonella Typhimurium and Enteritidis dominate global human salmonellosis cases, despite regional differences in prevalence. 

NCBI PD link for serovar Typhimurium: https://www.ncbi.nlm.nih.gov/pathogens/isolates/#(taxgroup_name:%22Salmonella%20enterica%22)%20AND%20computed_types:(%22serotype=Typhimurium%22)

Genetic characteristics: 

Salmonella Typhimurium has been found to be polyphyletic with four lineages identified. According to den Bakker et al. (2011) classification, Salmonella Typhimurium belongs to clade A of Salmonella enterica. This serovar is classified according to the susceptibility to typing phages (, in definite phage typing types (PTDT)); one common PT DT (PT104DT104) was typically has been found to have resistance to ampicillin, chloramphenicol, streptomycin, sulphonamide and tetracycline (ACSSuT resistance type). In England, two outbreaks caused by a multidrug - resistant (MDR) strain (ASSuTTm resistant type) strain of S. Typhimurium DT120 occurred in 2011.

Animal reservoir: serovar Typhimurium is found in multiple animal species, including cattle, chickens, turkey, swine, wild animals and insects.

Geographical distribution: serovar Typhimurium is widely distributed. In the multiple locations (i.e., US, the EU, Africa and Latin America) this serovar is the second most common serovar. In Oceania is the most common serovar. In Asia is among the ten most common serovars.

Outbreaks: numerous of outbreaks have been associated with serovar Typhimurium. Outbreaks have been linked to a number of foods and also been linked to contact with live poultry (chicks, ducklings, and other live baby poultry). Here we mention the latest outbreaks caused by this serovar.

A review paper concluded that lineages of S. Typhimurium was associated with different sequence types (STs). While ST19 exhibits a broad host range and commonly causes gastroenteritis in humans, the host-restricted ST313 is predominantly associated with invasive bloodstream infections in sub-Saharan Africa. According to EnteroBase, ST19 accounts for 86% of available S. Typhimurium genomes, whereas ST313 represents only 7%. Epidemic ST19 strains encompass multiple phage types, including DT104 (mainly cattle), DT193/DT120 and U288 (primarily swine), DT8 (ducks/geese), and DT160 (wild birds). Recent advances in genomic classification have introduced a hierarchical clustering (HC) system for Salmonella based on single nucleotide variations (SNVs). At the serotype-defining level (HC900), most S. Typhimurium isolates cluster within HC900_2, with a minority assigned to HC900_6511 and HC900_6910.

Most of the strains of Relevant genetic characteristics: Whole genome sequences for 27 strains of S. Typhimurium have been deposited at GenBank as for October, 2013. Genomic characteristics of the sequenced S. Typhimurium include i) a genome size ranging from 4.82- 5.09 Mb, ii) a mol G+C% of approx. 52.2, and iii) 4,556-5,619 genes. Typically, strains of S. Typhimurium contain a plasmid of approx. 90 kb that carry virulence genes (Salmonella virulence plasmid spv operon (SVP)). Large resistant plasmids of approx. 200 kb , representing that represented different incompatibility types (e.g., IncHI1), have also been identified in the sequenced strains S. Typhimurium. Prophages and genomic islands are important genomic components of serovar Typhimurium; for example, S. Typhimurium str. LT2 has four prophages (Fels-1, Fels-2, Gifsy-1, and Gifsy-2); within S. Typhimurium strains, the prophage content shows variation. Pathogenicity islands (SPIs) are found in all S. Typhimurium sequenced to date, including this include SPIs-1 to 6, 9, 11 to 14, and 16; being SPI14 SPI-14 specific to S. Typhimurium. In addition, genomic island content shows variationsome genomic islands are strain-specific; for example, S. Typhimurium MDR strain ST1660/06 has three strain-specific genomic islands encoding that encode putative virulence and resistance genes. Genomic islands carrying that encode antibiotic resistance appear to be a common feature of a number of S. Typhimurium MDR strains, these genomic islands include, e.g., Salmonella genomic island 1 (SGI1) described in S. Typhimurium DT104 and genomic island GI-DT12 in S. Typhimurium T000240. The latest genomic island (GI-DT12) contains antibiotic resistance genes (i.e., bla(oxa-30), aadA1, qacEΔ1, and sul1, mercury resistance proteins, cat, and tetA) and virulence genes (i.e., the aerobactin iron-acquisition siderophore system (lutA and lucABC), and an iron transporter (sitABCD)). Similarly, another study found that all S. Typhimurium ST313 isolates collected from Nigeria and the Democratic Republic of Congo carried resistance genes, including blaTEM1b, catA1, strA/B, sul1, and dfrA1, along with the aac(6')1aa gene. Phylogenetic analysis showed that Congolese and Nigerian isolates—from both blood and stool—were closely related. Furthermore, comparative genomic analysis uncovered a unique virulence-associated fragment (ST313-TD) shared exclusively by S. Typhimurium ST313 and S. Dublin.

In Sub-Sahara regions of Africa, invasive strains of S. Typhimurium emerged, single nucleotide polymorphism (SNP)-based phylogeny of this these invasive strains and strains from other regions, showed two lineages of invasive strains that clustered together. According to den Bakker et al. (2011) classification, Salmonella Typhimurium belongs to clade A.

Genome sequences available:

Okoro et al. estimated that these lineages emerged independently around 52 and 35 years ago, closely coinciding with the onset of the current HIV pandemic. The shift from lineage I to lineage II isolates may have been driven by clonal replacement, possibly influenced by chloramphenicol use in treating invasive NTS disease. 

Schultz et al. revealed that infection with S. Typhimurium enhances susceptibility to intestinal inflammation in both DSS-treated and IL-10^−/− mice. This heightened vulnerability is linked to the bacterium's ability to persist in the liver and spleen, a process mediated by virulence factors secreted through the type III secretion system encoded by Salmonella Pathogenicity Island 2 (SPI-2/T3SS-2). While vaccination with a live attenuated vaccine moderately reduced the susceptibility of IL-10^−/− mice to S. Typhimurium-induced intestinal inflammation, it failed to eliminate bacterial persistence in these tissues. During 4 to 6 weeks of chronic infections of S. Typhimurium, one mouse harbored phenotypically distinct adapted clones in the spleen versus liver, demonstrating tissue-specific bacterial evolution. Meanwhile, three co-housed mice became intestinally colonized by an identical clone containing a conserved non-synonymous mutation in kdgR (a metabolic transcriptional regulator), strongly suggesting cross-mouse transmission. Phylogenetic tracking revealed this mutation emerged in an index mouse within 14 days post-infection before spreading to two cage-mates. Subsequent challenge experiments confirmed this kdgR-variant possesses superior intestinal colonization capacity compared to wild-type, providing direct evidence of adaptive evolution enhancing enteric fitness. 

Animal reservoir: Serovar Typhimurium is host-generalists that can colonize and cause diseases in multiple animal species, including but not limited to cattle, poultry, swine, wild animals, and insects.

Geographical distribution: Serovar Typhimurium is globally distributed. During the study period from 2001 to 2007, Salmonella Typhimurium were the second most prevalent Salmonella serovars isolated from human in most regions, except in North America and Oceania (Australia and New Zealand). In these two regions, Salmonella Typhimurium was the most frequently reported in humans. Among human Salmonella isolates, serovar Typhimurium accounted for 17.1% of cases (ranging from 15% in 2007 to 18.9% in 2001).

Human outbreaks: Numerous outbreaks have been associated with S. Typhimurium. Human outbreaks have been linked to a number of foods and to contact with animals (chicks, ducklings, and other live animals). Below are some examples.

¹ Multiple serovars, including Salmonella Altona, Cerro, Enteritidis, Indiana, Infantis, Johannesburg, Mbandaka, and Typhimurium, were linked to this outbreak. The case number represents the total number of cases associated with the outbreak and does not specifically indicate the number of people infected by Salmonella Typhimurium.

² A total of 228 Salmonella Typhimurium and 33 Salmonella Newport infections were reported in 24 states.

Border rejections: Multiple border rejections linked to Salmonella Typhimurium have been reported. The majority of them are associated with poultry and poultry products. Below are some examples. 

¹ Salmonella Gaminara, Agona, Typhimurium, Infantis, Rubislaw, and Saintpaul were found.

² Salmonella Typhimurium and Newport were found. 

Recalls: Multiple recalls linked to Salmonella Typhimurium have been reported. They are associated with a variety of food commodities.

¹ This recall was caused by a multistate outbreak described above. Importers issued a recall for American/slicer cucumbers produced by Agrotato, S.A. de C.V. in Sonora, Mexico, which were sold during October and November 2024.

² This recall was caused by a multi-country outbreak in Europe described above.

³ This recall was caused by a multistate outbreak described above. Peanut Corporation of America’s Blakely, GA and TX issued a recall of their commercially distributed peanut butter.

Relevant links:

1. https://academic.oup.com/jac/article-abstract/51/1/180/771276?redirectedFrom=fulltext
2. https://www.liebertpub.com/doi/10.1089/fpd.2008.0213?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed
3. https://www.microbiologyresearch.org/deliver/fulltext/micro/171/1/mic001521.pdf?itemId=/content/journal/micro/10.1099/mic.0.001521&mimeType=application/pdf#:~:text=xylose%20lysine%20deoxycholate.-,TAXONOMY,before%20the%20Kauffmann–White%20scheme.
4. https://www.sciencedirect.com/science/article/pii/S1286457901013752?via%3Dihub
5. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.01368/full
6. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2025.1547190/full
7. https://bmcgenomics.biomedcentral.com/articles/10.1186/1471-2164-12-425
8. https://academic.oup.com/jac/article/46/1/7/695645
9. https://www.liebertpub.com/doi/abs/10.1089/fpd.2013.1513#utm_source=ETOC&utm_medium=email&utm_campaign=fpd
10. https://pubmed
11. Salmonella enterica subsp. enterica serovar Typhimurium str. LT2 http://www.ncbi.nlm.nih.gov/assembly/28528/
12. Salmonella enterica subsp. enterica serovar Typhimurium str. 14028S http://www.ncbi.nlm.nih.gov/assembly/359508/
13. Salmonella enterica subsp. enterica serovar Typhimurium str. 798 http://www.ncbi.nlm.nih.gov/assembly/368468/
14. Salmonella enterica subsp. enterica serovar Typhimurium str. D23580 http://www.ncbi.nlm.nih.gov/assembly/359488/
15. Salmonella enterica subsp. enterica serovar Typhimurium str. SL1344 http://www.ncbi.nlm.nih.gov/assembly/445688/
16. Salmonella enterica subsp. enterica serovar Typhimurium str. ST4/74 http://www.ncbi.nlm.nih.gov/assembly/378298/
17. Salmonella enterica subsp. enterica serovar Typhimurium str. T000240 http://www.ncbi.nlm.nih.gov/assembly/407038/
18. Salmonella enterica subsp. enterica serovar Typhimurium str. U288 http://www.ncbi.nlm.nih.gov/assembly/608548/
19. Salmonella enterica subsp. enterica serovar Typhimurium str. UK1 http://www.ncbi.nlm.nih.gov/assembly/360258/
20. Salmonella enterica subsp. enterica serovar Typhimurium var-5 str. CFSAN001921 http://www.ncbi.nlm.nih.gov/assembly/41141/
21. Salmonella enterica subsp. enterica serovar Typhimurium str. ST1489 http://www.ncbi.nlm.nih.gov/assembly20146749/
22. https:/62931/www.nature.com/articles/35101614
23. httpsSalmonella enterica subsp. enterica serovar Typhimurium str. ST1660/06 http://wwwpubmed.ncbi.nlm.nih.gov/assembly/54683823105062/Salmonella enterica subsp. enterica serovar Typhimurium str. ST4848
24. httphttps://wwwpubmed.ncbi.nlm.nih.gov/assembly21098248/64311/Salmonella enterica
25. https subsp. enterica serovar Typhimurium str. ST78896 http://wwwpubmed.ncbi.nlm.nih.gov/assembly24129621/62921/Salmonella enterica subsp. enterica serovar Typhimurium str. STm1
26. httpshttp://wwwpubmed.ncbi.nlm.nih.gov/assembly/49342823023330/Salmonella enterica subsp. enterica serovar Typhimurium str. STm10 http
27. https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2018.01166/full
28. https://bmcmicrobiol.biomedcentral.com/articles/10.1186/s12866-016-0646-2
29. https://pmc.ncbi.nlm.nih.gov/assembly/503588/Salmonella enterica subsp. enterica serovar Typhimurium str. STm11 http://www.ncbi.nlm.nih.gov/assemblyarticles/503608PMC127920/Salmonella enterica subsp. enterica serovar Typhimurium str. STm12 http
30. https://www.liebertpub.com/doi/10.1089/fpd.2010.0787?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed
31. httpsncbi.nlm.nih.gov/assembly/503628/Salmonella enterica subsp. enterica serovar Typhimurium str. STm2 http://www.ncbicdc.nlm.nih.gov/assembly/499908/Salmonella enterica subsp. enterica serovar Typhimurium str. STm3 httpsalmonella/outbreaks/cucumbers-11-24/index.html
32. https://www.ncbicdc.nlm.nih.gov/salmonella/assembly/503528/Salmonella enterica subsp. enterica serovar Typhimurium str. STm4 httpoutbreaks/backyardpoultry-05-24/investigation.html#:~:text=As%20of%20June%2020%2C%202024,No%20deaths%20have%20been%20reported.
33. https://www.ncbi.nlm.nih.gov/assembly/503548/
34. Salmonella enterica subsp. enterica serovar Typhimurium str. STm5 http://www.ncbi.nlm.nih.gov/assembly/503648/
35. Salmonella enterica subsp. enterica serovar Typhimurium str. STm6 http://www.ncbi.nlm.nih.gov/assembly/503568/
36. Salmonella enterica subsp. enterica serovar Typhimurium str. STm7 http://www.ncbi.nlm.nih.gov/assembly/47901/
37. Salmonella enterica subsp. enterica serovar Typhimurium str. STm8 http://www.ncbi.nlm.nih.gov/assembly/503508/
38. Salmonella enterica subsp. enterica serovar Typhimurium str. STm9 http://www.ncbi.nlm.nih.gov/assembly/506978/
39. Salmonella enterica subsp. enterica serovar Typhimurium str. TN061786 http://www.ncbi.nlm.nih.gov/assembly/356608/

Relevant links:

1. food-safety.com/articles/10195-salmonella-outbreak-linked-to-sprouts-sickened-509-people-over-two-years-in-ten-european-countries
2. https://archive.cdc.gov/www_cdc_gov/salmonella/typhimurium-02-18/index.html
3. https://archive.cdc.gov/www_cdc_gov/salmonella/typhimurium-03-18/index.html
4. https://archive.cdc.gov/www_cdc_gov/salmonella/typhimurium-live-poultry-04-13/index.html
5. https://marlerclark.com/macomb-county-salmonella-outbreak-traced-to-ground-beef#:~:text=At%20least%2022%20people%20from,for%20Disease%20Control%20and%20Prevention.
6. https://www.cbc.ca/news/canada/ottawa/salmonella-found-in-ottawa-caterer-s-ground-beef-1.1150870#:~:text=Social%20Sharing,week%20while%20the%20investigation%20continues.
7. https://archive.cdc.gov/www_cdc_gov/salmonella/typhimurium-hedgehogs-09-12/index.html#:~:text=of%20this%20outbreak.-,A%20total%20of%2026%20persons%20infected%20with%20the%20outbreak%20strain,%2C%20and%20Washington%20(7).
8. https://archive.cdc.gov/www_cdc_gov/salmonella/typhimurium-cantaloupe-08-12/index.html#:~:text=illness%20is%20reported.-,Recall,although%20further%20shipment%20was%20likely.
9. https://archive.cdc.gov/www_cdc_gov/salmonella/2011/ground-beef-2-1-2012.html#:~:text=The%20outbreak%20strain%20of%20Salmonella,Salmonella%20Infection%20for%20more%20details.
10. https://archive.cdc.gov/www_cdc_gov/salmonella/2011/water-frog-7-20-2011.html
11. https://wwwhttp://online.liebertpub.com/doi/abs/10.1089/fpd.2013.1513#utm_source=ETOC&utm_medium=email&utm_campaign=fpd
12. http://www.nature.com/nature/journal/v413/n6858/full/413852a0.html
13. http://www.ncbi.nlm.nih.gov/pubmed/23023330
14. http://www.ncbi.nlm.nih.gov/pubmed/23105062
15. http://www.ncbi.nlm.nih.gov/pubmed/21622747
16. http://www.ncbi.nlm.nih.gov/pubmed/24129621
17. http://www.biomedcentral.com/1471-2164/12/425
18. 1513#:~:text=Between%20July%20and%20September%202011,two%20discrete%20but%20linked%20outbreaks.
19. https://pubmed.ncbi.nlm.nih.gov/23611032/
20. https://outbreakdatabase.com/outbreaks/canterbury-england-unknown-2009
21. https://archive.cdc.gov/www_cdc_gov/salmonella/2009/peanut-butter-2008-2009.html
22. https://webgate.ec.europa.eu/rasff-window/screen/notification/745843
23. https://webgate.ec.europa.eu/rasff-window/screen/notification/673450
24. https://webgate.ec.europa.eu/rasff-window/screen/notification/613462
25. https://webgate.ec.europa.eu/rasff-window/screen/notification/466440
26. https://webgate.ec.europa.eu/rasff-window/screen/notification/522451
27. https://webgate.ec.europa.eu/rasff-window/screen/notification/423186
28. https://www.fda.gov/food/outbreaks-foodborne-illness/outbreak-investigation-salmonella-cucumbers-november-2024
29. https://webgate.ec.europa.eu/rasff-window/screen/notification/643944
30. https://webgate.ec.europa.eu/rasff-window/screen/notification/558911
31. https://webgate.ec.europa.eu/rasff-window/screen/notification/471210
32. https://marlerclark.com/news_events/salmon#:~:text=Peanut%20Corporation%20of%20America%20Peanut%20Butter%20Salmonella%20Outbreak%20Lawsuits%20%2D%20Nationwide,PCAhttp://www.ncbi.nlm.nih.gov/pubmed/21098248