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Background: 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. S. Montevideo is the sixth most common serovar isolated from humans and animals in the U.S. Outbreaks caused by S. Montevideo have been associated with imported spices and live poultry. Whole genome sequencing of a number of S. Montevideo strains have been conducted, including an study that identified one strain with two large plasmids that encoded antimicrobial and heavy metal resistance genes.  

Animal reservoir: Cattle and chickens are common reservoirs of S. Montevideo.

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.

NCBI PD link for serovar Montevideo: https://www.ncbi.nlm.nih.gov/pathogens/isolates/#(taxgroup_name:%22Salmonella%20enterica%22)%20AND%20computed_types:(%22serotype=Montevideo%22)

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. Geographical distribution: S. Montevideo is globally distributed. It has been reported, among the most common serovars, in the U.S., Europe, Latin America, Asia, and Oceania

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

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) andMbandaka (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.

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 examplesRecalls: Food recalls have been associated with S. Montevideo.

Relevant links and references:

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.

Relevant links:

1. https://jamanetwork.com/journals/jamapediatrics/article-abstract/495402
2. https://stacks.cdc.gov/view/cdc/152396/cdc_152396_DS1.pdf
3. https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2019.00102/full
4. https://journals.asm.org/doi/10.1128/mbio.01913-24
5. https://www.nature.com/articles/srep46232
6. https://www.microbiologyresearch.org/content/journal/mgen/10.1099/mgen.0.000202
7. https://pubmed.ncbi.nlm.nih.gov/23566273/
8. https://www.nature.com/articles/srep46232#:~:text=Abstract,poultry%20or%20poultry%20meat%20products.
9. http://www.jbjc.org/en/article/doi/10.3784/j.issn.1003-9961.2014.12.022
10. https://www.sciencedirect.com/science/article/pii/S0362028X23068151
11. https://archive.cdc.gov/#/details?url=https://http://www.cdc.gov/salmonella/montevideo-tahini01-05-1318/index.html
12. https/http://wwwarchive.cdc.gov/www_cdc_gov/salmonella/montevideo-0603-1216/index.htmlhttp
13. https://archive.cdc.gov/#/details?url=https://www.cdc.gov/salmonella/montevideo-tahini-05-13/index.html
14. httphttps://wwwarchive.eurosurveillancecdc.org/ViewArticle.aspx?ArticleId=20040httpgov/#/details?url=https://www.cdc.gov/salmonella/montevideo-0306-1612/index.htmlhttp
15. https://www..eurosurveillance.org/content/10.2807/ese.16.50.20040-en
16. https://pmc.ncbi.nlm.nih.gov/articles/PMC2870340/
17. https://pubmed.ncbi.nlm.nih.gov/12501260/
18. https://pubmed.ncbi.nlm.nih.gov/10491878/
19. https://webgate.ec.europa.eu/rasff-window/screen/notification/723009
20. https://webgate.ec.europa.eu/rasff-window/screen/notification/702610
21. https://webgate.ec.europa.eu/rasff-window/screen/notification/685839
22. https://webgate.ec.europa.eu/rasff-window/screen/notification/473167
23. https://webgate.ec.europa.eu/rasff-window/screen/notification/726067
24. https://webgate.ec.europa.eu/rasff-window/screen/notification/657396
25. https://webgate.ec.europa.eu/rasff-window/screen/notification/607162
26. https://webgate.ec.europa.eu/rasff-window/screen/notification/603115foodsafetynews.com/2013/05/salmonella-linked-to-tahini-sickens-8-across-country/#.WVvXMPnyuUl