Salmonella Heidelberg

Background: Salmonella enterica subsp. enterica serovar Heidelberg (antigenic formula 1,4,[5],12:r:1,2) is a serovar of the O:4 (B) serogroup. S. Heidelberg is commonly found in poultry meat in North America. In the U.S. and Canada, it has caused numerous infections in chickens. In the U.S., this serovar has caused a number of outbreaks that included the recent outbreak (October, 2013), linked to raw chicken; this outbreak was caused by a multidrug resistant S. Heidelberg strain (resistant to ampicillin, chloramphenicol, gentamicin, kanamycin, streptomycin, sulfisoxazole, and tetracycline). S. Heidelberg accounts for the 8.6% of ceftriaxone-resistant Salmonella isolated from humans in the U.S. Recently, a phage typing scheme was developed for serovar Heidelberg in Canada; this scheme recognizes 49 phage types.

Animal reservoir: S. Heidelberg is mostly found in chickens and turkeys. It has also been found in dogs.

Geographical distribution: Mostly reported from North America, serovar Heidelberg is the second and seventh most common serovar isolated from humans in Canada and in the U.S., respectively. In Europe this serovar is rare (approx. 180 cases/year).

Relevant genetic characteristics: Whole genome sequences for 15 strains of S. Heidelberg have been deposited at GenBank as of October, 2013. Genomic characteristics of the sequenced S. Heidelberg include (i) a genome size ranging from 4.73 to 4.98 Mb, (ii) a mol G+C% of 52.1, and (iii) 5,578 to 5,039 predicted genes. Many of these sequenced strains have been implicated in recent outbreaks (2011 and 2012), in the U.S. Salmonella Heidelberg str. SARA33 is a multidrug resistant 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, blaOXA-2 and blaTEM, 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.

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.

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
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
2001	Australia	Eggs	12

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.

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Salmonella Heidelberg