Grass-fed and antibiotic- and growth-hormone-free cattle at Kookoolan Farm in Yamhill, Ore., in April. (Don Ryan/Associated Press)

OVER THE decades that bacteria have been exposed to antibiotics, they evolved methods to resist the drugs, creating a serious problem for modern medicine. Without antibiotics, some illnesses may become untreatable. Unfortunately, antibiotics have been badly overused both for people and in animal agriculture. Recent research shows that bacteria can share their resistance skills with other bacteria through mobile genes. The news out of China and Denmark in recent weeks has been disturbing.

On Nov. 18, Chinese researchers reported discovery of a “major increase” in resistance to the antibiotic colistin. While a relatively old antibiotic with side effects, colistin has been in demand as a last-resort antibiotic when some others failed to work. Colistin is largely used for human health in the United States; if it stops working, that would leave a big hole. The resistance mechanism to colistin was carried on a plasmid, a kind of bus for genetic material, given the designation MCR-1. It sits on a mobile piece of DNA that can be transferred from one bacterium to another.

Then, on Dec. 3, researchers in Denmark reported another shocker. Looking back over the genetic blueprints they had already made of some 3,000 bacteria, they found MCR-1 present in one human patient, from this year, and in five food samples imported from 2012 to 2014. Advances in genomics made this rapid surveillance possible. Although unanswered questions remain, the implication is that the mobile gene conferring resistance to colistin is circling the globe.

Antibiotics have long been used to help farm animals grow larger and faster on the same amount of feed, and to prevent disease in a flock or herd. The industry insisted this practice had little overlap with drugs important to human health. But the recent research suggests once again that bacteria in pigs in China can trade mobile resistance genes with a bacteria that might infect a human in the United States or Denmark. The pathways between humans and animals are not entirely clear, but the fact of the exchange of genes that confer resistance capability is significant and has shown up in other research as well. A new report from a United Kingdom group studying antibiotic use on the farm, published Tuesday, declared: “we believe that there is sufficient evidence showing that the world needs to start curtailing the quantities of antimicrobials used in agriculture now.”

Many laudable efforts are underway to reduce the use of antibiotics; agriculture must be an essential part of this effort. The Food and Drug Administration has wisely persuaded drugmakers to end sales of antibiotics that are important to human health for growth promotion in animals by 2016 and strengthened veterinary oversight. However, the FDA will continue to permit the use of some antibiotics for disease prevention in animals that are not sick, and the FDA’s latest data show an uptick in antibiotic use on the farm. More needs to be done to reverse this trend. Antibiotics are a common resource for all humanity. They must be saved from overuse and obsolesence.