Professor of molecular bacteriology at the University of Bristol, Matthew Avison,, explains the link between antibiotic resistance in animals and humans.
The links between antibiotic usage in food-producing animals and antibiotic resistance in humans is the source of much debate, but increasingly, scientific evidence shows most human drug-resistant infections are arising from human medical use of antibiotics.
This is not to say the farming industry can become complacent. There is no doubt that, historically, farmers and vets have overused antibiotics to mask management and disease problems and, as a result, are being blamed for much of the problem with antibiotic resistance.
The classic case is campylobacter food poisoning from under-cooked chicken. High use of fluoroquinolones in poultry in the past has undoubtedly increased the amount of fluoroquinolone resistance in campylobacter isolated from human infections.
However, the poultry industry has taken massive steps to address this problem and is leading the way in antibiotic use reduction.
For other types of antibiotic resistance, it is a much more complicated issue. Pathogens such as E.coli and MRSA can be picked up from animals, but do not necessarily cause a problem straight away.
Only under certain circumstances do these ‘opportunistic pathogens’ cause disease. For example, they can infect a wound of the urinary tract, and this is particularly a problem in older or more vulnerable people.
The more often a person encounters resistant bacteria from animals, the more likely it is they will cause a resistant infection. But most people in developed countries do not interact closely with farmed animals, so the chance of this happening is low.
Of more concern is the fact that, in some instances, bits of genetic material can move from one bacterium to another.
For example, resistant bacteria from a pig could pass on resistance to human bacteria in the gut, meaning there does not always need to be prolonged interaction with resistant animal bacteria to make animal-derived resistance a problem for humans.
However, evidence from studying human infections shows even this type of transmission is unlikely.
While cases of death or prolonged illness in humans that can be traced back to antibiotic resistant bacteria which have arisen in farmed animals are rare, any such cases are too many. Therefore, all sectors have a responsibility to work together to tackle the problem.
There is, of course, also the issue that antibiotic resistance in animal bacteria potentially makes disease in animals more difficult to treat, which has implications for animal welfare and food production.
On a positive note, raising the profile of antibiotic resistance has made the farming industry take a long hard look at itself and identify where there is scope for change.
From my perspective I think farmers and vets need to work together to reduce antibiotic use in a smarter, more targeted way, which is cost-effective and does not compromise animal welfare.
But there is not a lot of evidence that simply reducing the use of antibiotics will lead to a large reduction in resistance, particularly in complex production systems where there is lots of potential for cycling of resistant bacteria on-farm.
To do this, farmers may also need to change and improve biosecurity and management practices.
The farming industry has made great strides in demonstrating it is taking antimicrobial resistance seriously and is reducing is antibiotic usage.
Continuing to do so will hopefully reduce pressure on the industry and ensure it does not continue to take a disproportionate amount of blame for what is a major global issue.