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A new study by the Ineos Oxford Institute for antimicrobial research , University of Oxford, reveals that industrial poultry farming has led to more than 100-fold increase in the movement of Campylobacter , allowing strains that once circulated in wild birds to mix extensively in commercial poultry populations.
Campylobacter is the most common bacterial cause of diarrhoea worldwide, causing more than 3.5 times as many gastroenteritis cases in the UK each year as all other monitored foodborne bacteria combined. Rising rates of antimicrobial resistance (AMR), which occurs when bacteria resist drugs designed to kill them, are making Campylobacter infections increasingly difficult to treat.
In the new study, published in the Proceedings of the National Academy of Sciences (PNAS), researchers analysed nearly 2,800 bacterial genomes collected from chickens and wild birds in 30 countries (including UK and USA) between 1979 and 2024. They found that the huge global expansion of chicken farming has created ideal conditions for the bacterium to spread, mix and acquire new traits that help it survive.
Since the 1960s, global chicken numbers have increased seven-fold to approximately 31 billion birds. Today, chickens account for around 70% of all bird biomass on earth. While this increase in numbers has led to the production of affordable animal protein at scale, it has also created ideal conditions for bacteria to adapt and spread.
Using genomic analyses, the researchers identified genetic changes in Campylobacter that were associated with adaptation to the chicken environment. These included genes involved in antimicrobial resistance, oxidative stress tolerance, metal acquisition and motility, and traits that can help bacteria survive and thrive in modern poultry production systems.
Professor Sam Sheppard , Professor of Microbial Genomics and Evolution, University of Oxford and senior author of the paper said : “Industrial farming has created one of the largest animal habitats on the planet. Our findings provide new evidence that human-driven environmental change can increase the spread of infectious diseases.
“As chicken populations have grown, bacteria that were once largely confined to wild birds have gained far more opportunities to enter poultry flocks, spread and become established. Understanding these evolutionary consequences is essential if we are to reduce future risks from zoonotic disease and antimicrobial resistance.”
The study also suggests that vast, densely populated chicken flocks may act as ecological ‘pathogen sponges’, absorbing and amplifying bacterial strains from multiple sources. Mathematical modelling showed that once chicken populations reach a critical scale, strains originating in wild birds can become self-sustaining within poultry populations, even when poorly adapted to their new host.
A previous study from the IOI found that 80% of human Campylobacter infections in Oxfordshire are associated with poultry meat, and that many of these infections are resistant to antibiotics.
Oakem Kyne , DPhil student, University of Oxford and first author of the paper said: “As Campylobacter strains adapt to life in poultry, they can acquire traits that help them survive in challenging environments, including traits linked to antimicrobial resistance. Understanding how farming practices influence bacterial evolution is an important step towards reducing the burden of foodborne disease.”
Notes to editors:
For media enquiries and interview requests, contact Sean Bromilow, Ineos Oxford Institute: sean.bromilow@chem.ox.ac.uk
The paper ‘Accelerating Campylobacter zoonosis in the Anthropocene’ will be published by Proceedings of the National Academy of Science on or after 20:00 BST / 15:00 ET Monday 27 July, DOI 10.1073/pnas.2609969123. Advance copies of the paper can be read under embargo via the Proceedings of the National Academy of Sciences embargoed tipsheet on EurekAlert . Journalists should register with EurekAlert at https://www.eurekalert.org/register and request access to PNAS materials.
About the Ineos Oxford Institute for antimicrobial research (IOI)
The Ineos Oxford Institute for antimicrobial research (IOI) is an antimicrobial discovery and development institute based at the University of Oxford. Established in 2021 through a generous gift from INEOS, researchers at the IOI are advancing new antimicrobial therapies from scientific discovery towards clinical development.
About the University of Oxford
Oxford University has been placed number 1 in the Times Higher Education World University Rankings for the tenth year running, and number 3 in the QS World Rankings 2024. At the heart of this success are the twin-pillars of our ground-breaking research and innovation and our distinctive educational offer.
Oxford is world-famous for research and teaching excellence and home to some of the most talented people from across the globe. Our work helps the lives of millions, solving real-world problems through a huge network of partnerships and collaborations. The breadth and interdisciplinary nature of our research alongside our personalised approach to teaching sparks imaginative and inventive insights and solutions.
Through its research commercialisation arm, Oxford University Innovation, Oxford is the highest university patent filer in the UK and is ranked first in the UK for university spinouts, having created more than 300 new companies since 1988. Over a third of these companies have been created in the past five years. The university is a catalyst for prosperity in Oxfordshire and the United Kingdom, contributing around £16.9 billion to the UK economy in 2021/22, and supports more than 90,400 full time jobs.
Proceedings of the National Academy of Sciences
Accelerating Campylobacter zoonosis in the Anthropocene
27-Jul-2026