Salmonella Livingstone

Background: Salmonella enterica subsp. enterica serovar Livingstone (antigenic formula 6,7,14:d:l,w) is a serovar of the O:7 (C₁) serogroup. This serovar was first isolated in 1951 from human feces in UK. From 1999 to 2003, there was a huge surge in the isolation of serovar Livingstone from human salmonellosis infections and animal-based food products in Tunisia. During 1989-1991, serovar Livingstone was the third most prevalent Salmonella serotype isolated from human salmonellosis infections in the Tayside area of Scotland.

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

Genetic characteristics: Serovar Livingstone has been found to be polyphyletic with four lineages identified and one stand-alone singleton that does not cluster with any other Salmonella Livingstone isolates. In a nosocomial outbreak associated with serovar Livingstone in Tunisia, all outbreak strains (n=16) exhibited resistance to ceftriaxone and ceftazidime, mediated by the production of an extended-spectrum β-lactamase (ESBL). Additionally, they showed resistance to multiple aminoglycosides (kanamycin, tobramycin, netilmicin, gentamicin, and amikacin) as well as sulfamethoxazole-trimethoprim. The ESBL resistance was encoded on a 40-kb conjugative plasmid. Genetic analysis revealed the presence of the mobile insertion sequence ISEcp1 upstream of bla_CTX-M-27, positioned similarly to its arrangement in bla_CTX-M-14. A novel trimethoprim resistance gene, dfrA21, was identified on a 90-kb plasmid. This gene was integrated as a single resistance cassette within a class I integron. Li et al. identified five clades of serovar Livingstone, with evidence suggesting that the global animal feed trade likely facilitated their introduction into China. Among these, Clade-5-I-a/b—the predominant lineage in China—demonstrated invasiveness in murine, avian (chicken), and zebrafish infection models. Antimicrobial susceptibility testing indicated that the vast majority (>96%) of Chinese Livingstone isolates exhibited multidrug resistance. In a comparative study, all Tunisian isolates exhibited resistance to amoxicillin, amoxicillin-clavulanic acid, ticarcillin, cefalotin, gentamicin, and kanamycin, as well as to third-generation cephalosporins (cefotaxime and ceftazidime). In contrast, Belgian isolates remained susceptible to all tested antibiotics. Genotypically, the Tunisian isolates were homogeneous, belonging exclusively to sequence type ST543, whereas the Belgian isolates exhibited greater diversity with eight strains typed as ST543, two as ST638, and one as ST457. All isolates including them from Tunisia and Belgium carried five chromosomal genes (agfA, hin/H2, iroB, phoP/Q, and slyA) but lacked the plasmid-encoded spvA and spvC.

Animal reservoir: Poultry is likely to be a potential reservoir for serovar Livingstone.

Geographical distribution: Serovar Livingstone has been reported worldwide.

Human outbreaks:

Year	Location	Associated source	Number of cases
2023-2024	US: Utah	Restaurant-related (no common source was identified)	11
2002	Tunisia	Nosocomial	16
2001	Norway, Sweden	Processed fish products	44 in Norway, 16 In Sweden
1989-1991	Scotland	Not identified	71

Animal outbreaks:

Year	Location	Breed	Number of cases
1980	UK	CBA/ca mice	60¹

¹ Only mice under 3 weeks old exhibited symptoms of enteritis. They were treated orally with tetracycline, 10 g/L drinking water for 10 days.

Border rejections:

Year	Exporting country	Importing country	Associated source	Product category
2020	US	Greece	Fish meal	Feed materials

Recalls:

Year	Location	Recalled food	Type
2024	Slovakia	Rucola from Italy	Fruits and vegetables
2020	Poland	Hulled sesame seeds¹	Nuts, nut products and seeds

¹ Salmonella Amsterdam and Salmonella Livingstone were found in sesame seeds from India, packed in Poland.

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Salmonella Livingstone