Antibiotic-resistant genes are widespread in nature, study finds


Interaction of methicillin-resistant staphylococcus aureus, MRSA, with a human white cell: Scientists discovered antibiotic-resistant genes like MRSA in 71 environments including oceans and human feces. (Rocky Mountain Laboratories/NIAID/NIH)

From Antarctic lakes to forest soil in Puerto Rico to the guts of mice, scientists are finding antibiotic-resistant genes almost everywhere they look, according to a new study that examined environmental samples from around the globe.

The findings, published Thursday in the journal Current Biology, revealed how widespread antibiotic-resistant genes are in nature. They also raised questions about how the prevalence of resistant genes might relate to a major health problem: bacterial infections in humans that increasingly don’t respond to antibiotics.

“While the environment is known to harbor antibiotic-resistant strains of bacteria, as proven by many preceding studies, we did not really know the extent of their abundance,” Joseph Nesme, one of the study’s authors and a researcher at the University of Lyon in France, said in an announcement about the findings.

To try to determine the prevalence of antibiotic-resistant genes, scientists tapped into a growing reservoir of public data to compare DNA samples found in nature with those of “superbugs” that have infected patients in hospitals. Ultimately, researchers discovered antibiotic-resistant genes in 71 environments, from human feces to English prairies.

Scientists have long known that antibiotic-resistant genes are present in nature. Such organisms existed long before human beings began using bacteria in the environment to help produce the life-saving antibiotics now used throughout the world.

Antibiotic resistance isn’t just a hospital phenomenon.

Most of the genes are benign, with little potential for making the leap to animals and humans. But sometimes that transfer does happen.

“What we’re seeing more and more of, that’s unquestionably true, is that these resistant genes are becoming more and more abundant in pathogens” that can then carry antibiotic resistance to new organisms, said Lance Price, an epidemiologist and expert in antibiotic resistance at George Washington University. “They are getting incorporated into organisms that they never were in before.”

Once that happens, resistant genes tend to thrive and multiply, given their ability to adapt and to stand up to certain antibiotics. Scientists are working to decipher precisely how — and how often — resistant genes in nature find their way into pathogens such as E. coli that can carry them on to humans and animals, with grave health consequences.

“It is only with more knowledge on antibiotic resistance dissemination” — from the environment to the clinic — “that we will be able to produce more sustainable antibiotic drugs,” Nesme said.

The publication of the study comes amid mounting concern that the planet could be barreling toward a post-antibiotic era in which common infections might once again prove fatal as the antibiotics used to treat them become less and less effective.

“The problem is so serious that it threatens the achievements of modern medicine,” the World Health Organization concluded in a report last week.

The WHO documented “very high rates of resistance” in different parts of the globe: Some urinary tract infections and skin wounds, once easily treatable with common antibiotics, are proving more and more difficult to defeat. The bacteria that cause pneumonia are now less susceptible to penicillin. In dozens of countries, the last-resort treatment for gonorrhea is losing its punch. Meanwhile, few new antibiotics are in the development pipeline.

Despite the prevalence of antibiotic-resistant genes in nature, Price said that the growing threats in human medicine are largely rooted in human misuse of antibiotics, and that the solutions lie in human hands.

In September, the Centers for Disease Control and Prevention warned that the nation faces “potentially catastrophic consequences” if it does not move rapidly to counter the growing threat of antibiotic-resistant infections, which sicken about 2 million Americans and kill an estimated 23,000 each year.

The agency noted that the overuse of antibiotics is the strongest contributing factor to the surge in resistance around the world — the more germs are exposed to an antibiotic, the more they are able to build resistance to it — and it has pushed for doctors and hospitals to be more judicious in their prescribing of the drugs.

At the same time, the overwhelming majority of antibiotics in the United States are used in animal agriculture, both to promote growth and to treat and prevent disease in livestock. In December, the Food and Drug Administration asked the agricultural industry to voluntarily phase out the use of certain antibiotics in livestock and prevent their use merely to boost animal growth. The move was intended to address long-standing fears that the massive amounts of antibiotics being used on farms were making those medications less effective over time.

Brady Dennis is a national reporter for The Washington Post, focusing on food and drug issues.
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