Researchers at Michigan State University have warned that unchecked use of antibiotics in world agriculture is accelerating the development of antibiotic resistance.

Microbiology professor James Tiedje said that the increasing production and use of antibiotics, about half of which is used in animal production, is mirrored by the growing number of antibiotic resistance genes (ARGs), effectively reducing antibiotics' ability to fend off diseases in animals and humans.

He said a lack of monitoring of antibiotics use on farms in China – the world's largest producer and consumer of antibiotics – as well as a number of other countries, risks creating a serious global problem. A study, of which Professor Tiedje was a co-author, conducted on Chinese commercial pig farms, found 149 unique ARGs, some at levels 192 to 28,000 times higher than the control samples.

Professor Tiedje was part of a research team led by Yong-Guan Zhu of the Chinese Academy of Sciences, which made the discovery. He commented, "Our research took place in China, but it reflects what's happening in many places around the world. The World Organization for Animal Health and the U.S. Food and Drug Administration have been advocating for improved regulation of veterinary antibiotic use because those genes don't stay local."

Antibiotics in China are weakly regulated, and the country uses four times more antibiotics for veterinary use than the United States. Since the medicine is poorly absorbed by animals, much of it ends up in manure – an estimated 700 million tons annually in China alone. This is traditionally spread as fertiliser, sold as compost or can even enter watercourses or groundwater, taking with it ARGs. The MSU professor added that there are also other means of spreading ARGs, including international trade and recreational travel.

Daily exposure to antibiotics, such as those in animal feed, allows microbes carrying ARGs to thrive. In some cases, these antibiotic resistant genes become highly mobile, meaning they can be transferred to other bacteria that can cause illness in humans. This is of serious concern because the infections they cause can't be treated with antibiotics.

ARGs can reach the general population through food crops, drinking water and interactions with farm workers. Because of this undesirable cycle, ARGs pose a potential global risk to human health and should be classified as pollutants, said Tiedje.

The Danish government has made repeated requests to tighten up regulation of antimicrobial use in the EU, over alarming findings by its surveillance institutes.  

Study lead author Zhu also commented, "It is urgent that we protect the effectiveness of our current antibiotics because discovering new ones is extremely difficult. Multidrug resistance is a global problem and must be addressed in a comprehensive manner, and one area that needs to be addressed is more judicious use and management of wastes that contain ARGs."