Campaigners refute antibiotics study

Campaigners have questioned the validity of a University of Glasgow study, which concluded that farm animals are unlikely to be the major source of antibiotic resistance in humans.

The Soil Association has written to the Proceedings of the Royal Society B, where the study was published, claiming that the researchers left out important data and were misleading in the presentation of their findings.

Richard Young, a policy advisor at the Soil Assocation, told Meat Trades Journal: “They base their findings, in part, on the fact that, of 52 resistance profiles found in human isolates and of 35 resistance profiles found in animal isolates, only 22 were common to both humans and animals. The authors say this is fewer common profiles than one would expect if the two salmonella populations were well-mixed.

“However, it is clear from the supplementary data that the 22 common profiles accounted for 2,707 of the 2,761 (or 98%) of human isolates and for 2,418 of 2,439 (99%) of animal isolates. The overwhelming dominance of the common profiles is evidence supporting the opposite view — that the two salmonella populations are well mixed.”

The study also found that of the 22 common resistance profiles, 11 first appeared in humans, six simultaneously in humans and animals and five first in animals. However, the authors did not reveal which of the profiles emerged first in which species. “One resistance profile alone accounted for 90% of animal isolates and 70% of human isolates, and it would have been instructive to know whether it first emerged in humans or animals,” said Young.

He added that the fact that the authors left this data out suggested that it might have contradicted their theory. “If it supported their theory, then I would be surprised that they hadn’t used it,” he said.

Young said the Soil Association was concerned that the study had been used by the British Veterinary Association (BVA) as “incontrovertible evidence” that it was right to campaign against moves in Europe to restrict the use of antibiotics. He added that the Soil Association was not calling for veterinarians to be left without drugs for treating animals, but for the ban of prophylactic use of antibiotics.

“We believe that perhaps around 25% of the use of antibiotics that is going on in intensive pig and poultry farms is still effectively for growth promotion, even though it is used under the name of disease prevention. It is that particular aspect that we want to stamp out,” he said.

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