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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. While this serovar is very rare and hardly reported among human cases, it has caused two outbreaks (one in Norway and one in the UK). In the US 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 S. serovar Mikawasima in humans and animals in the last 10 years. In Malaysia, S. Mikawasima was reported from fish and from aquaculture systems; the reported strains showed resistant to up to four antibiotics (chloramphenicol, clindamycin, rifampicin, and tetracycline). 

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

Genetic characteristics: According to 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 same resistance gene profile [bla_TEM-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., bla_TEM-1B and bla_SHV-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: Reptiles and fish have been reported as a reservoir. Pigs and wild boars are the reservoirs for serovar Mikawasima. This serovar was also isolated from turtle. 

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

Human outbreaks: 

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

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Relevant links:

1. https://pubmed.ncbi.nlm.nih.gov/5600522/
2. https://www.ecdc.foodsafetynewseuropa.comeu/2019en/11publications-data/ukeuropean-bearssurveillance-brunt-of-multi-country-salmonella-outbreak/#google_vignettesystem-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.foodsafetynews.com/2018/09/rare-salmonella-strain-sickens-50-in-five-eu-countries/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://pubmedpmc.ncbi.nlm.nih.gov/8270007articles/PMC3298264/
9. https://webgatewww.ececdc.europa.eu/sites/rasff-windowdefault/screenfiles/notification/420202documents/SALM_AER_2019_Report_Final.pdf
10. httpshttp://www.geostrategicforecasting.com/proahedr-salmonellosis-serotype-mikawashima-2/httpcroris.hr/crosbi/publikacija/prilog-skup/729181
11. https://umexpertwww.um.edu.my/file/publication/00004462_86509.pdfhttpfoodsafetynews.com/2019/11/uk-bears-brunt-of-multi-country-salmonella-outbreak/#google_vignette
12. https://www.ncbi.nlm.nih.gov/pubmed/13889310foodsafetynews.com/2018/09/rare-salmonella-strain-sickens-50-in-five-eu-countries/
13. https://pubmed.ncbi.nlm.nih.gov/383304148270007/
14. https://wwwwebgate.ec.croriseuropa.hreu/crosbirasff-window/publikacijascreen/prilog-skupnotification/729181420202