Background: Salmonella enterica subsp. enterica serovar Mikawasima (antigenic formula 6,7,14:y:e,n,z15) is a serovar of the O:7 (C1) serogroup. Serovar Mikawasima was first isolated from tortoises in 1967 in Turkey. The first isolation of serovar Mikawasima within the EU/EEA was reported in 1976 as part of a large-scale investigation into Salmonella prevalence in Dutch pigs. Between 2007 and 2012, a total of 671 human serovar Mikawasima infections were reported to the European Surveillance System (TESSy) by EU/EEA countries. Case numbers in Europe have shown a consistent rise since 2009. Serovar Mikawasima cases showed a 92.1% increase over 2018 levels and a 137.1% surge compared to 2017. In US, there are no reports of serovar Mikawasima in humans and animals in the last 10 years. 

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

Genetic characteristics: Serovar Mikawasima has been found to be polyphyletic with three lineages identified. According to Novak et al. (2024), all the outbreak-related isolates (n=75) were resistant to ampicillin and gentamicin. Most isolates (98%) showed resistance to amoxicillin/clavulanic acid, third-generation cephalosporins (36% to ceftriaxone and 47% to ceftazidime) and 40% of the isolates exhibited extended-spectrum β-lactamase production. In addition, whole-genome sequencing (WGS) analysis revealed that three outbreak-related strains (ST2030) have the same resistance gene profile [blaTEM-1B, aac(6')-Iaa, aac(6')-Im, and aph(2'')-Ib)]. Ferencak et al. identified persistence Mikawasima strain in the University Hospital of Split and found that all sequenced isolates belonged to ST2030 and carried aminoglycoside (e.g., aac(6′)-Iaa, and aac(6′)-Im) and ESBL resistance (e.g., blaTEM-1B and blaSHV-2) determinants, with 10% showing an MDR phenotype. Detected virulence genes (e.g., mig-14) associated with biofilm formation imply possible nosocomial adaptation.

Edwards et al. found that serovar Mikawasima, in addition to its standard y and e,n,z15 phases, naturally expressed two extra H antigens—z47 and z50—previously observed in Arizonae-group serovars. These four antigens showed no serological relatedness but could interconvert through both induced and spontaneous phase variation.

Animal reservoir: Pigs and wild boars are the reservoirs for serovar Mikawasima. This serovar was also isolated from turtle. 

Geographical distribution: Serovar Mikawasima appears to be frequently found in Europe especially Spain but occasionally in other continents such as Asia and North America.

Human outbreaks: 

Year

Location

Associated source

Number of cases

2020-2021Croatia Unknown27
2019Europe: multi-countryUnknown192
2018Europe: multi-countryUnknown50

2013

UK

Unknown

75

2012

Norway

Unknown

13

1992

UK

Doner kebab

9

Border rejections: There have been no recent border rejections linked to this serovar. 

Recalls: 

YearLocationRecalled foodType
2020NorwayOrganic Little gem lettuce from SpainFruits and vegetables

Relevant links:

  1. https://pubmed.ncbi.nlm.nih.gov/5600522/
  2. https://www.ecdc.europa.eu/en/publications-data/european-surveillance-system-tessy
  3. https://pubmed.ncbi.nlm.nih.gov/38330414/
  4. https://www.mdpi.com/2076-0817/14/5/408
  5. https://pubmed.ncbi.nlm.nih.gov/13889310/
  6. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2025.1547190/full#h10
  7. https://www.ecdc.europa.eu/sites/default/files/media/en/publications/Publications/RRA-unusual-increase-salmonella-mikawasima-cases-in-EU-EEA-28-november-2013.pdf
  8. https://pmc.ncbi.nlm.nih.gov/articles/PMC3298264/
  9. https://www.ecdc.europa.eu/sites/default/files/documents/SALM_AER_2019_Report_Final.pdf
  10. https://www.croris.hr/crosbi/publikacija/prilog-skup/729181
  11. https://www.foodsafetynews.com/2019/11/uk-bears-brunt-of-multi-country-salmonella-outbreak/#google_vignette
  12. https://www.foodsafetynews.com/2018/09/rare-salmonella-strain-sickens-50-in-five-eu-countries/
  13. https://pubmed.ncbi.nlm.nih.gov/8270007/
  14. https://webgate.ec.europa.eu/rasff-window/screen/notification/420202
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