Salmonella Typhimurium

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.

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 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)).

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.

Animal reservoir: Serovar Typhimurium is found in multiple animal species, including cattle, poultry, swine, wild animals, dogs, and insects.

Geographical distribution: Serovar Typhimurium is globaly distributed. In multiple locations (i.e., U.S., Europe, Africa and Latin America), it is reported as the second most common Salmonella serovar in humans. In Australia, it is the most common serovar in humans. In Asia, it is among the ten most common serovars in humans.

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
2024-2025	US: multistate	Cucumbers	113
2024	US-multistate	Backyard poultry	409^a
2018	US-multistate	Chicken salad	265
2018	US-multistate	Dried Coconut	14
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

^a Multiple serovars, including Salmonella Altona, Cerro, Enteritidis, Indiana, Infantis, Johannesburg, Mbandaka, and Typhimurium, were linked to this outbreak. The case number represents the total number of cases associated with the outbreak and does not specifically indicate the number of people infected by Salmonella Typhimurium.

Border rejections: Multiple border rejections linked to Salmonella Typhimurium have been reported. The majority of them are associated with poultry and poultry products. Below are some examples.

Year	Exporting country	Importing country	Associated source	Product category
2025	Brazil	Netherlands	Frozen chicken meat	Poultry meat and poultry meat products
2024	Brazil	Portugal	Chicken gizzards	Poultry meat and poultry meat products
2023	Brazil	Netherlands	Fresh chicken meat	Poultry meat and poultry meat products
2021	Brazil	Germany	Black pepper¹	Herbs and spices
2021	Cameroon	Finland	Chilled waterleaves (Talinum triangulare)	Fruits and vegetables
2020	India	Germany	Dog chews (dried tripes)²	Feed materials

¹ Salmonella Gaminara, Agona, Typhimurium, Infantis, Rubislaw, and Saintpaul were found.

² Salmonella Typhimurium and Newport were found.

Recalls: Multiple recalls linked to Salmonella Typhimurium have been reported.

Year	Location	Recalled food	Type
2024-2025	US: multistate	Cucumbers¹	Fruits and vegetables
2023-2025	Europe: multi-country	Alfalfa sprouts²	Fruits and vegetables
2023	Romania	Turkey meat from Hungary	Poultry meat and poultry meat products
2022	Ireland	Milled brown flaxseed from UK	Nuts, nut products and seeds
2022	Multiple countries	Chocolate³	Confectionery
2021	Norway	Pork sides with jaw from Germany	Meat and meat products (other than poultry)

¹ This recall was caused by a multistate outbreak described above. Importers issued a recall for American/slicer cucumbers produced by Agrotato, S.A. de C.V. in Sonora, Mexico, which were sold during October and November 2024.

² This recall was caused by a multi-country outbreak in Europe described above.

³ This recall was caused by a multi-country outbreak described above. Kinder Chocolate Eggs, traced back to a factory in Belgium, were identified as the vehicle.

Relevant links:

https://www.cdc.gov/salmonella/outbreaks/cucumbers-11-24/index.html

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Salmonella Typhimurium