Industrial poultry farming has driven a dramatic rise in one of the world's most common food-poisoning bacteria, with researchers warning that modern farming practices have created ideal conditions for dangerous strains to spread and become harder to treat. Scientists at the University of Oxford say the rapid expansion of global chicken production has transformed the evolution of Campylobacter, a bacterium responsible for millions of cases of diarrhoea each year and the leading bacterial cause of food poisoning worldwide. Chicken Boom Drives Bacterial Spread Researchers analysed almost 2,800 bacterial genomes collected from chickens and wild birds across 30 countries between 1979 and 2024. Their findings suggest the seven-fold increase in global chicken numbers since the 1960s has enabled Campylobacter to spread more than 100-fold. The study found that bacteria originally circulating in wild birds have become established within commercial poultry populations, where dense flocks allow them to spread rapidly and evolve. Resistance Raises New Concerns Scientists identified genetic changes linked to antimicrobial resistance, making some infections increasingly difficult to treat. They also found adaptations that help the bacteria survive inside modern intensive poultry production systems. Researchers warned that once poultry populations reach sufficient scale, these bacterial strains can sustain themselves without relying on repeated transmission from wild birds. Huge Flocks Act as 'Pathogen Sponges' The study suggests large commercial chicken farms effectively act as ecological "pathogen sponges", absorbing bacteria from multiple sources before amplifying and spreading them further. Lead researcher Oakem Kyne said bacteria adapting to poultry environments can develop traits that improve survival, including resistance to antibiotics, highlighting the importance of understanding how farming practices influence disease evolution. Growing Challenge for Public Health Senior author Professor Sam Sheppard said the findings demonstrate how human-driven environmental change can accelerate the spread of infectious diseases and increase the threat posed by antimicrobial resistance. The warning comes as chickens now account for around 70% of all bird biomass on Earth. Previous Oxford research also found that around 80% of human Campylobacter infections in Oxfordshire were linked to poultry meat, with many strains already showing resistance to commonly used antibiotics, underlining the growing challenge facing public health and food safety. Poultry farming leads to 100-fold increase in food-poisoning bacteria, study finds
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