Background: Salmonella enterica subsp. enterica serovar Typhimurium (antigenic formula 4,5,12:i:1,2) is a serovar of the O:4 (B) serogroup. S. Typhimurium is a widely distributed serovar, representing which represent the second most common serovar isolated from humans in the United States and the European Union. This serovar belongs to the serogroup O:4 (B), there Europe. 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 in Africa. This serovar is classified according to the susceptibility to typing phages (phage typing (PT)); one common PT (PT104) 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) (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 globaly distributed. In the multiple locations (i.e., US, the EUU.S., Europe, Africa and Latin America) this serovar it is reported as the second most common Salmonella serovar. In Oceania Australia it is the most common serovar. In Asia it 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 animals (chicks, ducklings, and other live baby poultry). Here we mention some of the latest outbreaks caused by this serovar.
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Relevant genetic characteristics: Whole genome sequences for 27 strains of S. Typhimurium have been deposited at GenBank as for of October, 2013. Genomic characteristics of the sequenced S. Typhimurium strains 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 -to 5,619 predicted 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 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 . Among 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 SPI-14 specific to S. Typhimurium. In addition, genomic island content shows variation; 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 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)).
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 that clustered together. According to den Bakker et al. (2011) classification, Salmonella Typhimurium belongs to clade A.
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