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Humans spread antimicrobial resistant bacteria to urban wildlife

For the first time, a highly transmissible strain of the antibiotic-resistant superbug MRSA, which is currently plaguing hospitals in Northern Europe, has been isolated from hedgehogs in Helsinki. 

Superbugs such as Methicillin-resistant Staphylococcus aureus (MRSA) are antibiotic-resistant bacteria for which there are little or no available treatments. 

Recently, European hedgehogs, a common wild species living in urban areas, were found to be natural carriers of MRSA. Surveys in Denmark and Sweden suggest that up to 60 percent of hedgehogs carry a type of MRSA called mecC-MRSA, which causes 1 in 200 of all MRSA infections in humans.

The findings suggest a spillover of antimicrobial resistant (AMR) bacteria and genes to urban wildlife. This trend should be monitored to limit the emergence of antimicrobial resistance traits in the future. Worldwide spread of these antibiotic-resistant genes is a growing concern because they often target “last resort” classes of antibiotics.

Escherichia coli (E. coli) and Klebsiella pneumoniae bacteria are common in the intestines of healthy people and animals. Highly resistant strains with extended spectrum beta-lactamase-producing Enterobacteriaceae (ESBL-E) can cause urinary tract infections in people. ESBL-E are common in wild European hedgehogs, but little is known about Finnish hedgehogs specifically. 

To find out, the researchers tested samples from 115 dead hedgehogs in Finland between 2020 and 2021. Swabs and samples were obtained from each hedgehog to be tested for ESBL-E. Whole genome sequencing was used to examine the genomic features of the bacteria including resistant genes.

The research team found that 10 percent of hedgehogs had at least one MRSA-producing bacterial strain and at least one ESBL-producing strain.

Only three hedgehogs carried the type of MRSA called mecC-MRSA, commonly found in Sweden and Denmark, and has emerged in human patients in Northern Europe over the last few years. This suggests there is genetic diversity between MRSA strains over hedgehog populations and countries.

Furthermore, two E. coli strains identified in hedgehogs were human-associated types, suggesting that they could have transferred from humans to hedgehogs.

Venla Johansson from the University of Helsinki, who noted that it’s not just hedgehogs that carry antibiotic-resistant bacteria. 

“All wildlife and livestock carry many different types of bacteria, so there are many candidates for its dispersal in urban environments including humans themselves,” explained Johansson.

“Moreover, anthropogenic sources, such as waste, agriculture runoff and domestic wastewater have been linked to antimicrobial resistance transmission to wild animals.”

This observational study only sampled hedgehogs from one city in Finland, which means that the findings might not be representative of the whole country.

“In the future, the carriage of MRSA should be monitored from hedgehogs in different environments and in wider geographical context to determine whether hedgehogs could act as an AMR sentinel revealing AMR levels in the environment,” said Johansson.

The researchers of a previous study published in Nature emphasize that the findings are not a reason to fear hedgehogs, as humans rarely get infections with mecC-MRSA, even though it has been present in hedgehogs for more than 200 years.

The study was presented at this year’s European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) in Lisbon, Portugal.

By Katherine Bucko, Staff Writer

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