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, which represent the second most common serovar isolated from humans in the United States and 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 countries in Africa. This serovar is classified according to the susceptibility to typing phages, in definite phage types (DT); one common DT (DT104) 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) of S. Typhimurium DT120 occurred in 2011.
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In Sub-Sahara regions of Africa invasive strains of S. Typhimurium emerged, single nucleotide polymorphism (SNP)-based phylogeny of 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.
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