A new study by the Ineos Oxford Institute for antimicrobial research, University of Oxford, reveals that industrial poultry farming has led to more than a 100-fold increase in the movement of Campylobacter, allowing strains that once circulated in wild birds to mix extensively in commercial poultry populations, according to a July 27 statement.
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 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 production of affordable animal protein at scale, it has also created ideal conditions for bacteria to adapt and spread.
Using genomic analyses, researchers identified genetic changes in Campylobacter associated with adaptation to the chicken environment. These included genes involved in antimicrobial resistance, oxidative stress tolerance, metal acquisition and motility—traits that can help bacteria survive and thrive in modern poultry production systems.
Oakem Kyne, DPhil student at 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."
