Antibiotic-resistant bacteria spread from farms to wild birds

Jim Crocker
16th November, 2025

Antibiotic-resistant bacteria spread from farms to wild birds

Location of São Camilo State Park, situated in the municipality of Palotina, state of Paraná, Brazil, highlighting the mist nets (black arrows) placed throughout the study.

Image adapted from: Ribas et al. / CC BY (Source)

Key Findings

  • In a Brazilian forest, researchers found Staphylococcus aureus in over 12% of wild birds sampled, including two cases of MRSA
  • The MRSA found in birds is genetically linked to strains commonly found in pigs, suggesting spread from livestock to wildlife
  • While the MRSA strains carried genes for resistance to many antibiotics, they didn’t cause severe disease in lab tests, but have the potential to become more virulent
Antimicrobial resistance – the ability of microbes to resist the effects of drugs – is a growing global health concern. Bacteria like Staphylococcus aureus (often called ‘staph’) are particularly problematic, with some strains becoming resistant to many commonly used antibiotics. This resistance can make infections harder, and sometimes impossible, to treat. Understanding how these resistant strains spread is crucial to controlling their impact. A recent study by researchers at the Federal University of Santa Catarina (UFSC)[1] investigated this issue in a unique environment: a protected forest in Brazil. The study focused on wild birds in São Camilo State Park, an area of Atlantic Forest surrounded by farmland. Researchers collected samples from the mouths and throats of 197 birds representing 54 different species. They were looking for S. aureus and, importantly, whether the strains they found were resistant to antibiotics, specifically methicillin – a key indicator of resistance. Overall, S. aureus was found in 12.2% of the birds sampled. Of these, two were identified as Methicillin-resistant S. aureus (MRSA), meaning the bacteria could survive exposure to methicillin and related antibiotics. The remaining 27 isolates were Methicillin-susceptible S. aureus (MSSA). The discovery of MRSA in wild birds is significant. Previous research has shown that MRSA isn’t limited to human hospitals; it’s also found in livestock[2] and wild animals[3]. The UFSC study identified both MRSA strains as belonging to a specific genetic lineage called ST398. This is particularly noteworthy because ST398 is commonly found in pigs and other livestock – a ‘livestock-associated’ strain[4]. This finding strongly suggests that the MRSA found in the birds originated in agricultural settings and spread into the wild. The MRSA strains identified in the study possessed a wide range of genes conferring resistance to multiple antibiotics. This ‘resistome’ – the collection of all resistance genes – included resistance to beta-lactams (like penicillin), macrolides, and other important drug classes. Interestingly, the MSSA strains also showed high levels of resistance to macrolides, lincosamides, and streptogramin B antibiotics, with a significant proportion carrying the blaZ gene which confers resistance to penicillin. The presence of the scn gene was also frequently observed in the resistant isolates. While the MRSA strains carried many resistance genes, laboratory tests using wax moth larvae (Galleria mellonella) indicated they weren’t particularly virulent – meaning they didn’t cause severe disease in this model. However, the presence of a ‘virulome’ – a collection of genes associated with causing disease – suggests the potential for increased virulence in the future. The researchers used genomic sequencing to trace the origins of the MRSA strains. Their analysis showed a close genetic relationship between the MRSA found in the birds and MSSA strains isolated from swine in northeastern Brazil. This supports the idea of a ‘spillover’ event, where resistant bacteria from livestock spread into the wild bird population. This aligns with findings from other studies highlighting the role of livestock as a reservoir for antimicrobial resistance[4]. A study in Costa Rica also demonstrated the impact of human activities on antimicrobial resistance in wildlife, finding widespread resistance genes in various species[5]. The UFSC study builds on previous work showing that MRSA can be found in a variety of wild animals, including non-human primates, wild mammals, and rodents[3]. It adds to this body of knowledge by identifying a specific livestock-associated strain (ST398) in Brazilian wildlife for the first time. The findings emphasize the importance of a ‘One Health’ approach – recognizing the interconnectedness of human, animal, and environmental health – to address the growing threat of antimicrobial resistance. The study also highlights the vulnerability of fragmented ecosystems, like the Atlantic Forest, to the spread of antimicrobial resistance from human activities.

WildlifeHealthAnimal Science

References

Main Study

1) Emergence of Livestock‐Associated Methicillin‐Resistant Staphylococcus aureus ST398 in Wild Birds, Brazil

Published 11th November, 2025

https://doi.org/10.1002/mbo3.70131

Related Studies

2) Methicillin-Resistant Staphylococcus aureus (MRSA): One Health Perspective Approach to the Bacterium Epidemiology, Virulence Factors, Antibiotic-Resistance, and Zoonotic Impact.

https://doi.org/10.2147/IDR.S272733

3) Wild Animals Are Reservoirs and Sentinels of Staphylococcus aureus and MRSA Clones: A Problem with "One Health" Concern.

https://doi.org/10.3390/antibiotics10121556

4) Emergence of methicillin-resistant Staphylococcus aureus from clonal complex 398 with no livestock association in Brazil.

https://doi.org/10.1590/0074-02760170040

5) A multidisciplinary approach to analyze the antimicrobial resistance in natural ecosystems.

https://doi.org/10.1016/j.envres.2024.118549


Related Articles

An unhandled error has occurred. Reload 🗙