Antimicrobial resistance, when micro-organisms as bacteria, viruses and parasites, are no longer killed by formerly effective drugs. In the case of bacteria, concern has increased over the spread of resistance and the spectre of returning to the situation when many diseases affecting humans and animals were untreatable.

In humans, antimicrobial resistance is frequently attributed to veterinary use of antimicrobials. But the relative contribution to the problem by animals and humans is poorly understood at population levels. Despite this, proposals are under consideration by the European Parliament to phase out precautionary ( prophylactic) use of some antibiotics in animals in the hope the rate of increase in the occurrence of antimicrobial resistance would be slowed.

The plan is opposed by the British Veterinary Association, which says that the ban would compromise animal health and welfare.

Dr Alison Mather, (right) working with an interdisciplinary research team within the College of Medical,Veterinary and Life Sciences, used long-term surveillance data of Salmonella Typhimurium DT104 from co-located humans and animals in Scotland, to demonstrate how animal and human DT104 populations differ significantly in several ways, among them prevalence, linkage, time of emergence, and diversity.

Findings, published Proceedings of the Royal Society B, suggest local animal populations are unlikely to be a major source of resistance in humans, so questioning policies that restrict use of antimicrobials in local domestic animals. 

Professor Daniel Haydon, (left) director of the University of Glasgow’s Institute of Biodiversity Animal Health and Comparative Medicine, said: “In our study, there were significantly more human-only types of resistance than we might have expected if the animal and human microbial communities were well-mixed, suggesting that the risk of resistances passing from animals to humans is lower than previous research has indicated.

“In the majority of resistances which are common to both animals and humans, the resistances appeared first in humans. While it’s inevitable that contact, direct or indirect, between animals and humans will lead to some transmission of disease and resistance in both directions, it appears unlikely that the animal population is the major source of resistance diversity for humans.”

Professor Stuart Reid, senior work author, now Principal at the Royal Veterinary College, London,added: “It remains true that use of antimicrobials promotes resistance in microorganisms and of course we advocate prudent use in all species. But our work does call into question the, at times, singular focus on veterinary usage.

“Whilst our study has focused on a single bacterial species, our findings do demonstrate we must ensure that our local policies do not impact disproportionately on domestic livestock, without considering imported foodstuffs and animals abroad, as well as the medical use of antibiotics. There is still much to be done if we are to understand the problem at the level of the global ecosystem.”

The research was undertaken by the University of Glasgow, in partnership with Scottish Salmonella Shigella and Clostridium Difficile Reference Laboratory at Stobhill Hospital; Health Protection Scotland; the Public Health Agency of Canada and the University of Guelph in Canada.