Methicillin-resistant Staphylococcus aureus in wild European hedgehogs
In this research project we studied the occurrence of methicillin-resistant Staphylococcus aureus (MRSA) in wild European hedgehogs (Erinaceus europaeus) from urban Helsinki metropolitan area in 2020-2021.

Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to most beta-lactam antibiotics. MRSA is responsible for approximately 150,000 infections every year in the European Union (EU) causing significant mortality and increased health care costs. Although MRSA can be passed from human to animal and vice versa, in general human associated MRSA strains differ from those derived from domesticated and wild animals. Most of the MRSA strains in humans harbor the mecA gene, whereas mecC-harboring MRSA strains are widely distributed among different domesticated animal and wildlife species. mecC-MRSA is especially prevalent in European Hedgehogs due to co-evolutionary adaptation to penicillin-like substance-producing dermatophyte infection. Hedgehogs, commonly inhabiting areas with high human activity, can also be prone to acquiring antimicrobial resistance genes and bacteria from humans through various anthropogenic sources.

In our study we sampled deceased or euthanized wild hedgehogs from the Helsinki metropolitan area, Finland, brought to the Korkeasaari Zoo’s Wildlife Hospital during 2020 and 2021 due to injuries or other disease symptoms. Samples were screened for MRSA and confirmed isolates were characterized with whole genome sequencing. Genomic comparison was done against human derived MRSA isolates, to elucidate the origins of the hedgehog derived isolates.

The genomic comparison of the hedgehog and human derived MRSA isolates revealed a clonal dissemination of successful emerging mecA-MRSA t304/ST6 clone among humans and hedgehogs. This specific MRSA clone has recently emerged in Northern Europe among humans. Meanwhile, mecA-MRSA occurs only occasionally in wildlife and the occurrence of this specific clone in animal reservoirs is unknown. Additionally, the studied hedgehog derived mecA-MRSA isolates harbored human-specific genes, suggesting that these isolates could originate from humans. Further studies are needed to understand which factors leads to the spill back of MRSA from humans to wildlife.

The occurrence of mecC-MRSA was lower compared to previous studies done on wild hedgehogs. These results could indicate that eventually particular mecC-MRSA lineages were not distributed evenly among European hedgehog populations during the postglacial expansion in Europe or that other MRSA strains predominates among hedgehog populations in the Helsinki metropolitan area. However, wider geographical sampling of hedgehogs, using cultivation methods that can recover mecC-MRSA more efficiently should be carried in the future studies.

This study was conducted in collaboration with Korkeasaari Zoo Wildlife Hospital and The Finnish Institute for Health and Welfare (THL). This study was financially supported by the Academy of Finland (grant number 339417).

The published peer-reviewed article can be found at: