S. Montevideo¶

At a Glance


Antigenic Formula	`6,7,14:g,m,[p],s:[1,2,7]`
Serogroup	O:7 (C1)
NCBI Pathogen Detection	View isolates

Background Information¶

Salmonella enterica subsp. enterica serovar Montevideo (antigenic formula 6,7,14:g,m,[p],s:[1,2,7]) is a serovar of the O:7 (C₁) serogroup. This serovar was first isolated in Uruguay in 1936 from an infant with chronic enterocolitis. The Centers for Disease Control and Prevention (CDC) routinely includes serovar Montevideo among its top 20 Salmonella serotypes associated with human infections, causing an average of 700 illnesses in US each year. While serovar Montevideo ranked as the predominant Salmonella serotype in North America, it was not among the top five most reported serotypes in other continents.

Genetic Characteristics¶

Chen et al. found that serovar Montevideo is polyphyletic with four clades identified. Within the largest clade, Montevideo A, the subclade Montevideo A-10 was cattle-associated, whereas Montevideo A-7 was associated with environmental sources (e.g., water, sediment). The cattle-associated Montevideo-A-10 lineage (emerged ~1905) contained two clonal subclades, Montevideo-A-10-I (29% of isolates, emerged ~1968) and Montevideo-A-10-II (13% of isolates, emerged ~1958), both showing increased cattle-associated prevalence over time. Lalsiamthara and Lee used serovar Montevideo and Typhimurium to infect chickens and rabbits. They revealed that infected birds showed no visible signs of illness, and histopathology revealed only mild damage to intestinal epithelium and splenic parenchyma despite consistent serovar Montevideo isolation from these tissues. Salmonella Montevideo was internalized by chicken peritoneal macrophages at rates comparable to Salmonella Typhimurium but demonstrated greater susceptibility to chicken serum complement than rabbit serum. In mock-infected layers, serovar Montevideo caused transient internal egg contamination at trace levels, persisting for one week post-inoculation, suggesting infection of Salmonella Montevideo in chickens is asymptomatic and sub-clinical.

Nguyen et al. also identified four clades for serovar Montevideo in their study. They found that clade I strains have up to two large integrated mobile genetic elements (MGEs), each approximately 30–60 kb in size. A phage attachment site, known to be targeted by the lambdoid prophage Gifsy-2—a factor linked to virulence in Salmonella Typhimurium LT2 (which inserts between pepN and pcnB)—was found to be occupied by different prophages in Montevideo clades I and III (SM F7-F9). A prophage similar to Gifsy-1, Gifsy-2, or SEN34 (SM F8-F9), carrying the virulence genes gtgE and msgA but missing sodCI, was detected in all clade III strains except ATCC BAA710. Additionally, all clade IV strains contained Fels-2-like and Salmon_vB_SosS_Oslo-like prophages (SM F5 and SM F6, respectively), though these were not exclusive to clade IV. Furthermore, Montevideo isolates from all four clades were found to carry Salmonella pathogenicity islands (SPIs) with similarities to SPI-1 through SPI-6.

Animal Reservoir¶

Cattle and chicken are the main reservoirs for serovar Montevideo.

Geographical Distribution¶

Serovar Montevideo is globally distributed.

Human/Animal Outbreaks¶

Numerous outbreaks in different countries have been linked to serovar Montevideo, nuts have been associated with several of these outbreaks. Below are some examples.

Year	Location	Associated source	Number of cases
2020-2021	Canada	Restaurant kitchen drainage system	67
2018	US: multistate	Raw sprouts	10
2016	US: multistate	Pistachios¹	11
2013	US: multistate	Tahini²	16
2012	US: multistate	Live poultry	93
2009-2010	US: multistate	Red and black pepper/Italian-style meats³	272
2010	Germany	Dietary food supplement	15
2002	Australia & New Zealand	Tahini	68
2002	Japan	Lunch prepared by caterer	23
1995-1996	UK	Supermarket hot food outlet	NA

¹ There were a total of 11 people infected with the outbreak strains of Salmonella Montevideo (9 cases) and Senftenberg (2 cases) reported from nine states.

² Salmonella Montevideo (4 cases) and Mbandaka (12 cases) infections were reported from nine states.

³ Eleven people were infected by Salmonella Senftenberg. These 11 cases were not included in the overall case count (272).

Border Rejections¶

Multiple border rejections associated with serovar Montevideo have been reported. Below are some examples.

Year	Exporting country	Importing country	Associated source	Product category
2024	France	Italy	Rabbit meal for petfood production	Animal by-products
2024	Turkey	Germany	Dog chew¹	Pet food
2024	Turkey	Finland	Curry powder²	Herbs and spices
2021	Turkey	Finland	Potato seasoning³	Herbs and spices

¹ Salmonella Anatum, Brancaster and Montevideo were found.

² Salmonella Abony and Montevideo were found.

³ Salmonella Bredeney and Montevideo were found.

Recalls¶

Multiple recalls associated with serovar Montevideo have been reported. Below are some examples.

Year	Location	Recalled food	Type
2024	EU: multi-country	Hummus from Belgium	Nuts, nut products and seeds
2024	Germany	Dog chews from France	Feed materials
2023	Germany	Sesame paste from Turkey	Nuts, nut products and seeds
2023	EU: multi-country	Organic tahini from Germany, made with raw material from Turkey	Nuts, nut products and seeds
2016	US-multistate, Mexico, Canada, Peru	Pistachios¹	Nuts, nut products and seeds

¹ Wonderful Pistachios of Lost Hills, California issued a voluntary recalled. The recalled pistachios, distributed under the Wonderful, Paramount Farms, and Trader Joe’s brands, were sold across the US as well as in Canada, Mexico, and Peru.