S. Heidelberg¶

At a Glance


Antigenic Formula	`1,4,[5],12:r:1,2`
Serogroup	O:4 (B)
NCBI Pathogen Detection	View isolates

Background Information¶

Salmonella enterica subsp. enterica serovar Heidelberg (antigenic formula 1,4,[5],12:r:1,2) is a serovar of the O:4 (B) serogroup. Salmonella Heidelberg was first identified in 1933 in Heidelberg, Germany. It was later detected in the United States for the first time in 1954. In the United States, Salmonella Heidelberg ranks as the third most common serotype found in retail meat and food animal isolates. It is also among thetop four serotypesisolated from blood samples. Notably, 12%–13% of Salmonella Heidelberg infections in North America result in invasive disease, a rate significantly higher than the U.S. average of 7% for all Salmonella infections.

Genetic Characteristics¶

Serovar Heidelberg has been found to be monophyletic. Previously, 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.

Human/Animal Outbreaks¶

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

Year	Location	Associated source	Number of cases
2018-2019	Australia	Unidentified	59
2016	US: multistate	Contact with dairy calves	56
2013-2014	US: multistate	Raw chicken	634
2011	US: multistate	Kosher broiled chicken livers	190
2011	US: multistate	Ground turkey	136
2011	Europe	In-flight catering from Tanzania to Europe	22
2004	Canada	Food handler	32

Border Rejections¶

Year	Exporting country	Importing country	Associated source	Product category
2024	Brazil	Germany	Frozen chicken breast halves, salted	Poultry meat and poultry meat products
2024	Brazil	Germany	Poultry meat preparation	Poultry meat and poultry meat products
2023	Brazil	Czech Republic	Frozen chicken breast fillet	Poultry meat and poultry meat products

Recalls¶

Year	Location	Recalled food	Type
2014	US	Tyson mechanically separated chicken¹	Poultry meat and poultry meat products

¹ Tyson Foods, Inc. issued a recall of around 33,840 pounds of mechanically separated chicken products due to potential contamination with Salmonella Heidelberg. These products were manufactured on October 11, 2013, and distributed exclusively for institutional use across the nation.