Media

Food bug evolution uncovered

11 April 2008 


  • Food poisoning bacteria merging in agricultural environments
  • Free range ‘no increased infection risk’ for chickens


Two species of bacteria that are estimated to cause 400,000 cases of food poisoning in the UK (and about five times that number in the USA) every year are merging, probably as a result of agricultural activity, Oxford University scientists have discovered.

The research into the convergence, or ‘despeciation’ of Campylobacter jejuni and Campylobacter coli sheds light on the mysterious world of bacterial evolution and could help scientists understand where such diseases come from. A report of the research appears in this week’s Science.

‘Our evidence shows that Campylobacter jejuni and  Campylobacter coli are converging as a result of very recent exchanges of genetic material,’ said Professor Martin Maiden of Oxford University’s Department of Zoology who led the research. ‘It appears that recent ecological changes have removed the ‘species barrier’ between these two bacteria, enabling them to merge or ‘despeciate’. It’s highly plausible that this change is the unintended consequence of the introduction of intensive agricultural practices.’

While the convergence poses no immediate increased risk to humans, it does suggest that human activity shapes the development of many bacteria that cause illness in humans. Proper food preparation and cooking would still ensure that any infected meat is safe to eat.

Dr Daniel Falush, now of University College Cork, who collaborated with Professor Maiden’s Oxford team commented: ‘For bacterial evolution this is like observing Darwin’s finches: each species adapts to a particular ecological niche but as selection pressures change so these species may adapt or merge. What we are seeing is a similar thing happening at the level of microbes as environmental change driven by humans creates new ecological niches for bacteria – for instance in intensive farms or acidic areas around mines. Hopefully by understanding the processes at work we can limit the effect human activity has on the development of bacteria harmful to humans.’

Free range ‘no increased infection risk’ for chickens

In related research, an Oxford team led by Professor Maiden found that the free-range environment is not a major source for the infection of chickens with Campylobacter jejuni as had been widely assumed.

Chicken meat contaminated with C. jejuni is a major cause of food poisoning in humans. This has led to increased biosecurity measures that attempt to limit infection of chickens in intensive, housed conditions. It has been thought that free-range chickens are more at risk because they cannot be protected from outdoor infection sources such as wild birds.

‘It was widely thought that free-range chickens were likely to pick up Campylobacter from the free-range environment, particularly wild birds, but none of the evidence we have gathered supports this as a major infection source,’ said Professor Martin Maiden of Oxford University’s Department of Zoology. ‘If this was the case then you would expect to see free-range chickens sharing genetically similar bacteria with local wild bird populations but our study suggests that this is not the case. It’s good news as it means that not being able to extend comprehensive biosecurity measures to free-range poultry is probably not the threat to human health that had been feared.’  A total of 975 chickens from 64 flocks were sampled over a period of 10 months as part of the research. Wild bird populations in the areas concerned were also studied.A report of this research is due to appear in the journal Environmental Microbiology.

Both research projects were funded by the UK’s Department of Environment Food and Rural Affairs (DEFRA) and the UK’s Food Standards Agency.

For more information on either research project contact Professor Martin Maiden on +44 (0)1865 271284 or email martin.maiden@zoo.ox.ac.uk

Alternatively contact the University of Oxford Press Office on +44 (0)1865 283877 or email press.office@admin.ox.ac.uk

Notes to editors

  • A report of the research into bacterial evolution, entitled ‘Convergence of Campylobacter Species: Implications for Bacterial Evolution’, was published in Science on April 11 2008.
  • The bacterial evolution research was conducted by Professor Martin Maiden, Dr Daniel Falush, Dr Noel McCarthy and Dr Samuel Sheppard of the Departments of Zoology and Statistics at the University of Oxford.
  • A report of the research into free-range poultry, entitled ‘Campylobacter infection of broiler chickens in a free-range environment’, is to be published in the journal Environmental Microbiology.
  • The free-range poultry research was conducted by Professor Martin Maiden, Professor Marian Stamp Dawkins, Dr Frances Colles, Dr Noel McCarthy and Dr Samuel Sheppard of the Department of Zoology and Dr Kate Dingle and Dr Alison Cody of the Nuffield Department of Clinical Laboratory Sciences at the University of Oxford.