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Background: Salmonella enterica subsp. enterica serovar Typhimurium (antigenic formula 1,4,[5],12:i:1,2) is a serovar of the O:4 (B) serogroup. One variant named 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. 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:

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.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: Whole genome sequences for 27 strains of S. Typhimurium have been deposited at GenBank as 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. Most of the strains of of S. Typhimurium contain a plasmid of approx. 90 kb that carry virulence genes (Salmonella virulence plasmid (SVP)). Large resistant plasmids of approx. 200 kb that represented different incompatibility types (e.g., IncHI1), have also been identified in 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). Pathogenicity islands (SPIs) are found in all S. Typhimurium sequenced to date, this include SPIs-1 to 6, 9, 11 to 14, and 16; being SPI-14 specific to S. Typhimurium. In addition, some genomic islands are strain-specific; for example, S. Typhimurium MDR strain ST1660/06 has three strain-specific genomic islands that encode putative virulence and resistance genes. Genomic islands 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, cat, and tetA) and virulence genes (i.e., the aerobactin iron-acquisition siderophore system (lutA and lucABC), and an iron transporter (sitABCD)).

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