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

Year	Location	Associated source	Number of cases
2018	US-multistate	Chicken salad	265
2013	US-multistate	Live poultry	37
2013	US-multistate	Ground beef	22
2012	Canada	Ground beef	50
2012	US-multistate	Pet Hedgehogs	26
2012	US-multistate	Cantaloupe	261
2011	US-multistate	Ground beef	20
2011	US-multistate	African Dwarf Frogs	241
2011	England	Pork	51
2011	Ireland	Duck eggs	34
2010	US-multistate	Contact with water frogs	85
2009	England	unknown	14

Relevant 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 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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