Salmonella Typhimurium

Background: Salmonella enterica subsp. enterica serovar Typhimurium (antigenic formula 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 O:4 (B), there is one variant named S. Typhimurium var. Copenhagen, which lacks the factor 5 in the O antigen (4,12:i:1,2). This serovar was named Typhimurium because it produces "Typhi like symptoms in the murine model. S. Typhimurium has been used as model to understand the pathogenicity of Salmonella.  Serovar Typhimurium can cause disease in a wide range of hosts and invasive strains have been reported in some African countries. This serovar is classified according to the susceptibility to typing phages (phage typing (PT)); one common PT (PT104) was typically found to have resistance to ampicillin, chloramphenicol, streptomycin, sulphonamide and tetracycline (ACSSuT resistance type). In England two outbreaks caused by a multidrug-resistant (ASSuTTm) 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.

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). Large resistant plasmids of approx. 200 kb, representing different incompatibility types (e.g., IncHI1) have also been identified in the sequenced strains. 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 SPIs-1 to 6, 9, 11 to 14, and 16; being SPI14 specific to Typhimurium. In addition, genomic island content shows variation; for example, S. Typhimurium MDR strain ST1660/06 has three strain-specific genomic islands encoding putative virulence and resistance genes. Genomic islands carrying 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 GI-DT12 in S. Typhimurium T000240. The latest genomic island (GI-DT12) contains 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)).

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

Genome sequences available:

1. Salmonella enterica subsp. enterica serovar Typhimurium str. LT2 http://www.ncbi.nlm.nih.gov/assembly/28528/
2. Salmonella enterica subsp. enterica serovar Typhimurium str. 14028S http://www.ncbi.nlm.nih.gov/assembly/359508/
3. Salmonella enterica subsp. enterica serovar Typhimurium str. 798 http://www.ncbi.nlm.nih.gov/assembly/368468/
4. Salmonella enterica subsp. enterica serovar Typhimurium str. D23580 http://www.ncbi.nlm.nih.gov/assembly/359488/
5. Salmonella enterica subsp. enterica serovar Typhimurium str. SL1344 http://www.ncbi.nlm.nih.gov/assembly/445688/
6. Salmonella enterica subsp. enterica serovar Typhimurium str. ST4/74 http://www.ncbi.nlm.nih.gov/assembly/378298/
7. Salmonella enterica subsp. enterica serovar Typhimurium str. T000240 http://www.ncbi.nlm.nih.gov/assembly/407038/
8. Salmonella enterica subsp. enterica serovar Typhimurium str. U288 http://www.ncbi.nlm.nih.gov/assembly/608548/
9. Salmonella enterica subsp. enterica serovar Typhimurium str. UK1 http://www.ncbi.nlm.nih.gov/assembly/360258/
10. Salmonella enterica subsp. enterica serovar Typhimurium var-5 str. CFSAN001921 http://www.ncbi.nlm.nih.gov/assembly/41141/
11. Salmonella enterica subsp. enterica serovar Typhimurium str. ST1489 http://www.ncbi.nlm.nih.gov/assembly/62931/
12. Salmonella enterica subsp. enterica serovar Typhimurium str. ST1660/06 http://www.ncbi.nlm.nih.gov/assembly/546838/
13. Salmonella enterica subsp. enterica serovar Typhimurium str. ST4848 http://www.ncbi.nlm.nih.gov/assembly/64311/
14. Salmonella enterica subsp. enterica serovar Typhimurium str. ST78896 http://www.ncbi.nlm.nih.gov/assembly/62921/
15. Salmonella enterica subsp. enterica serovar Typhimurium str. STm1 http://www.ncbi.nlm.nih.gov/assembly/493428/
16. Salmonella enterica subsp. enterica serovar Typhimurium str. STm10 http://www.ncbi.nlm.nih.gov/assembly/503588/
17. Salmonella enterica subsp. enterica serovar Typhimurium str. STm11 http://www.ncbi.nlm.nih.gov/assembly/503608/
18. Salmonella enterica subsp. enterica serovar Typhimurium str. STm12 http://www.ncbi.nlm.nih.gov/assembly/503628/
19. Salmonella enterica subsp. enterica serovar Typhimurium str. STm2 http://www.ncbi.nlm.nih.gov/assembly/499908/
20. Salmonella enterica subsp. enterica serovar Typhimurium str. STm3 http://www.ncbi.nlm.nih.gov/assembly/503528/
21. Salmonella enterica subsp. enterica serovar Typhimurium str. STm4 http://www.ncbi.nlm.nih.gov/assembly/503548/
22. Salmonella enterica subsp. enterica serovar Typhimurium str. STm5 http://www.ncbi.nlm.nih.gov/assembly/503648/
23. Salmonella enterica subsp. enterica serovar Typhimurium str. STm6 http://www.ncbi.nlm.nih.gov/assembly/503568/
24. Salmonella enterica subsp. enterica serovar Typhimurium str. STm7 http://www.ncbi.nlm.nih.gov/assembly/47901/
25. Salmonella enterica subsp. enterica serovar Typhimurium str. STm8 http://www.ncbi.nlm.nih.gov/assembly/503508/
26. Salmonella enterica subsp. enterica serovar Typhimurium str. STm9 http://www.ncbi.nlm.nih.gov/assembly/506978/
27. Salmonella enterica subsp. enterica serovar Typhimurium str. TN061786 http://www.ncbi.nlm.nih.gov/assembly/356608/

Relevant links:

1. http://online.liebertpub.com/doi/abs/10.1089/fpd.2013.1513#utm_source=ETOC&utm_medium=email&utm_campaign=fpd
2. http://www.nature.com/nature/journal/v413/n6858/full/413852a0.html
3. http://www.ncbi.nlm.nih.gov/pubmed/23023330
4. http://www.ncbi.nlm.nih.gov/pubmed/23105062
5. http://www.ncbi.nlm.nih.gov/pubmed/21622747
6. http://www.ncbi.nlm.nih.gov/pubmed/24129621
7. http://www.biomedcentral.com/1471-2164/12/425
8. http://www.ncbi.nlm.nih.gov/pubmed/21098248

1.      http://www.ncbi.nlm.nih.gov/pubmed/20146749
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