New research provides evidence that antibiotic resistance has spread beyond hospitals and farms to wildlife
By Lindsey Konkel and Environmental Health News
WORCESTER, Mass. – One afternoon last winter, Julie Ellis unfurled a long, white tarp under a stand of trees near Coes Pond where hundreds of crows roost. Her mission: to collect as much bird poop as possible.
Back in the laboratory, Ellis’ colleagues combed through the feces. Testing its bacteria, they discovered something unusual – genes that make the crows resistant to antibiotics.
Drug-resistant infections are a fast-growing threat to human health, due largely to overuse of antibiotics in human medicine and livestock production, according to the Centers for Disease Control and Prevention. At least 2 million people each year in the United States alone are sickened by infections resistant to drugs.
Some experts worry that contaminating wildlife with such genes may hasten the spread of drug resistance. Nevertheless, the consequences for human health remain poorly understood.
“We’ve documented human-derived drug resistance where it shouldn’t be – in wildlife and the environment. But we know very little about how this may impact public health. There just isn’t that smoking gun,” said Ellis, a research scientist at Tufts University’s veterinary school.
In addition to crows, resistance genes have been detected in gulls, houseflies, moths,foxes, frogs, sharks and whales, as well as in sand and coastal water samples from California and Washington.
The spread to wildlife is “an indicator of the wide-reaching scale of the problem. Microbes connect the planet,” said Lance Price, a professor of environmental and occupational health at George Washington University.
“The danger is that we enter a post-antibiotic era in which even our last-line drugs won’t work and routine infections become life-threatening,” he said.
While antibiotics have revolutionized medicine in less than 100 years, antibiotic-producing bacteria have existed in nature for millions of years. Natural antibiotics likely evolved as weapons in a biological arms race between competing bacteria.
But the environmental drug resistance that Ellis and others are now seeing is different – it’s manmade.
“What has changed is that we’ve placed great selective pressure on bacteria with our use of antibiotics,” said Ludek Zurek, a microbiologist at Kansas State University who participated in the crow study.
Bacteria can swap genes with one another, so those that survive can pass along the genetic equipment to withstand an antibiotic assault to unrelated bacterial strains, spreading resistance across the globe, microbe by microbe.
“Those bacteria that pick up resistance genes survive better in an environment where antibiotics are being used. They can outcompete all the other bacteria,” said Price, who advocates against the use of antibiotics in livestock.
In the crow research, scientists collected nearly 600 fecal samples in four states – Massachusetts, Kansas, New York and California. Fifteen of the crows sampled, about 2.5 percent, harbored genes for resistance to vancomycin, a drug of last resort for hard-to-treat hospital-acquired infections. Crows with the resistance genes were found in all of the states except California.