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

Genetic characteristics: Serovar Heidelberg has been found to be monophyletic. Previously, a a phage typing scheme was developed for serovar Heidelberg in Canada; this scheme recognizes 49 phage types. S. Heidelberg accounts for the 8.6% of ceftriaxone-resistant Salmonella isolated from humans in the U.S. SARA33 is a multidrug resistant (MDR) strain. This strain was found, in silico, to contain a novel integron cassette; in addition, it was found to carry the following resistance genes: aac(6′)-ly, aadA5, aadB, aa(6′)-33, and aadA1, sul1 and sul2, bla_OXA-2 and bla_TEM, tetD. Resistance genes in S. Heidelberg have been identified in the chromosome (resistant islands) and in plasmids. Different incompatibility types (A/C, FIB, HI2) have been identified in the plasmids that carried resistance genes in S. Heidelberg. A MDR S. Heidelberg strain (resistant to ampicillin, chloramphenicol, gentamicin, kanamycin, streptomycin, sulfisoxazole, and tetracycline) was found to cause a multistate outbreak linked to the Foster Farms brand chicken. Etter et al. analyzed a total of nine Heidelberg isolates collected during the outbreak investigation and revealed that (i) six Salmonella Heidelberg isolates linked to the foodborne outbreak exhibited increased heat tolerance, (ii) one of these heat-tolerant isolates also demonstrated enhanced biofilm formation under stressful conditions, (iii) heat stress triggered higher expression of multidrug efflux and virulence genes in Salmonella Heidelberg, and (iv) the outbreak-related isolates appeared to be transcriptionally prepared to better withstand processing stresses and potentially to cause infection.

Phylogenetic and pan-genomic analyses that included two of the sequenced S. Heidelberg strains and other Salmonella serovars concluded that S. Heidelberg (i) belongs to clade A, according to den Bakker et al. (2011) classification, (ii) appears to have a single evolutionary origin, and (iii) contains 74 gene families unique to this serovar.  

Animal reservoir:Poultry, including chickens and turkeys, are the main reservoirs for serovar Heidelberg. It has also been found in other animals such as cattle, swine, and dogs.

Geographical distribution: Serovar Heidelberg has been reported worldwide, mainly in North America.

OutbreaksHuman outbreaks: Multiple Heidelberg outbreaks have been linked to poultry, most of them in the US. Here are some example:

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1. https://scholar.google.com/scholar_lookup?journal=J%20Bacteriol&title=About%20a%20new%20type%20of%20bacteria%20form%20the%20paratyphoid%20enteritis%20group&author=VH%20Habbs&publication_year=1933&pages=367-374&
2. https://www.jstor.org/stable/1588278?casa_token=sTneApEGY84AAAAA%3AxCcrraoy6aPu-M6ejq3MtxjBB1MMgP_Z6YwUi4_cVoYN9dHewNuMwxG9EeHAe6ua_dq1zAdT8vyzdTrmZ47-5_6uPGQhzNzzMViPBHNg6yfUnNVpvw&seq=1
3. https://pubmed.ncbi.nlm.nih.gov/18757574/
4. https://journals.asm.org/doi/10.1128/aac.01333-10
5. https://wwwnc.cdc.gov/eid/article/16/1/09-0729_article
6. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2025.1547190/full
7. https://journals.asm.org/doi/full/10.1128/jcm.41.9.4279-4284.2003
8. https://www.cdc.gov/salmonella/pdf/heidelberg-508c.pdf
9. https://pmc.ncbi.nlm.nih.gov/articles/PMC3790100/
10. https://pubmed.ncbi.nlm.nih.gov/23251446/
11. https://journals.asm.org/doi/10.1128/aem.01065-19
12. https://bmcgenomics.biomedcentral.com/articles/10.1186/1471-2164-12-425
13. https://pmc.ncbi.nlm.nih.gov/articles/PMC3175032/
14. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1282832/pdf#:~:text=Salmonella%20enterica%20subspecies%20enterica%20serovar%20Heidelberg%20(Salmonella%20Heidelberg)%20is%20primarily,Clothier%20and%20Byrne%2C%202016).
15. https://pmc.ncbi.nlm.nih.gov/articles/PMC3768931/
16. https://pubmed.ncbi.nlm.nih.gov/34932458/#:~:text=We%20report%20a%20multistate%20Salmonella,indicators%20of%20severity%20and%20invasiveness.
17. https://archive.cdc.gov/#/details?url=https://www.cdc.gov/salmonella/heidelberg-11-16/index.html
18. https://archive.cdc.gov/www_cdc_gov/salmonella/heidelberg-10-13/index.html
19. https://archive.cdc.gov/www_cdc_gov/salmonella/2011/chicken-liver-1-11-2012.html
20. https://pubmed.ncbi.nlm.nih.gov/25865382/
21. https://pmc.ncbi.nlm.nih.gov/articles/PMC9151100/
22. https://www.canada.ca/en/public-health/services/reports-publications/canada-communicable-disease-report-ccdr/monthly-issue/2005-31/restaurant-foodhandler-associated-outbreak-salmonella-heidelberg-gastroenteritis-identified-calls-local-telehealth-service-edmonton.html
23. https://webgate.ec.europa.eu/rasff-window/screen/notification/680242
24. https://webgate.ec.europa.eu/rasff-window/screen/notification/679279
25. https://webgate.ec.europa.eu/rasff-window/screen/notification/609282
26. https://archive.cdc.gov/www_cdc_gov/salmonella/heidelberg-01-14/advice-institutions.html