Salmonella Derby

Background: Salmonella enterica subsp. enterica serovar Derby (antigenic formula 1,4,[5],12:f,g:[1,2]) is a serovar of the O:4 (B) serogroup. This serovar was fist isolated from humans who were infected after eating contaminated pork pies in the UK in 1923. It is one of the dominant Salmonella serovars isolated from slaughter pigs in Europe, and ranks #4 in the most frequently isolated Salmonella serovars from clinical non-human sources in the United States.

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

Genetic characteristics: Serovar Derby has been found to be polyphyletic with seven lineages identified and two stand-alone singletons that do not cluster with any other Salmonella Derby isolates. Berni et al. identified a widespread and rapidly expanding lineage within the global Salmonella Derby population that is predominantly found in swine but is notably rare in humans. This lineage carries stop mutations in the SPI-1 genes sipA and hilC. Their results suggested that serovar Derby does not require the ability to invade the swine intestinal epithelium to circulate among pigs, resulting in the degradation of SPI-1. This decay of SPI-1, in turn, leads to its reduced virulence and attenuation in humans. Zheng et al. used CRISPRs typing and reported 35 new spacers in Salmonella Derby, with distinct spacer arrangements observed between ST40 and ST71 strains. Luo et al. found that two predominant sequence types (ST) of Salmonella Derby in China are ST40 and ST71, with ST40 currently being the most prevalent in Shenzhen. The phylogeny of serovar Derby are divided into five clades, and isolates from Shenzhen are primarily clustered in Clades 2, 4, and 5, showing closer genetic ties to strains from Asian countries (Thailand and Vietnam) than to those from Europe. Over an 11-year surveillance period in Shenzhen, Clades 2, 4, and 5 have emerged as the dominant epidemic branches, with Clades 2 and 5 exhibiting high levels of multidrug resistance. The most common resistance pattern observed is to ampicillin, tetracycline, ciprofloxacin, chloramphenicol, nalidixic acid, streptomycin, and sulfamethoxazole/trimethoprim.

Animal reservoir: The most common reservoir for serovar Derby is swine. However, it has also been reported in poultry, eggs and dairy products.

Geographical distribution: Serovar Derby has been reported worldwide such as the US, Europe, and China.

Human outbreaks: Multiple outbreaks linked to serovar Derby have been reported; in many of these outbreaks, the associated food was pork products. Below are examples.

Year	Location	Associated source	Number of cases
2013-2014	Germany	Raw fermented meat paste	145
2011	Spain	Dried pork sausage	<49
1973	Trinidad	Powdered infant formula	~3000
1963	US: multistate	Raw or under-cooked eggs	~822 (incl. secondary)

Border rejections: Multiple border rejections associated with serovar Derby have been reported. Here we selected two as examples.

Year	Exporting country	Importing country	Associated source	Product category
2022	Poland	Italy	Frozen turkey meat	Poultry meat and poultry meat products
2020	Spain	Italy	Frozen minced turkey breast¹	Poultry meat and poultry meat products

¹ Salmonella Derby and Bovismorbificans were both found.

Recalls: Multiple recalls linked to serovar Derby have been reported. Examples are below.

Year	Location	Recalled product	Type
2024	Finland	Frozen pork cheek from Poland via Estonia	Meat and meat products (other than poultry)
2022	Czech Republic	Frozen beef pet food from Germany¹	Pet food
2021	US	Salami stick²	Meat and meat products (other than poultry)

¹Salmonella Infantis, Derby, Reading and Enterobacteriaceae were found.

² Euro Foods has recalled around 119,091 pounds of Citterio brand Premium Italian-Style Salame Sticks products.

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Salmonella Derby