S. Mikawasima¶

At a Glance


Antigenic Formula	`6,7,14:y:e,n,z15`
Serogroup	O:7 (C1)
NCBI Pathogen Detection	View isolates

Background Information¶

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 fromtortoises 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.

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 [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¶

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/Animal Outbreaks¶

Year	Location	Associated source	Number of cases
2020-2021	Croatia	Unknown	27
2019	Europe: multi-country	Unknown	192
2018	Europe: multi-country	Unknown	50
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¶

Year	Location	Recalled food	Type
2020	Norway	Organic Little gem lettuce from Spain	Fruits and vegetables