Gene That Allows Bacteria to Fight Off Last Resort Drug Found in U.S. for First Time, Underscoring the Need to Stop Antibiotic Misuse in Livestock

Yesterday, news emerged that a gene which allows disease-causing bacteria to withstand colistin—an antibiotic used as a last-resort when all other antibiotics fail—was found in the United States for the first time.  The problem gene was found both in E. coli from a patient in Pennsylvania and in a sample taken from pig killed at a slaughter house.

In January, NRDC released an analysis showing the colistin resistance gene (known as mcr-1) is rapidly spreading around the world in meat, on animals and in humans. Today’s news adds one more country to the growing list.

The U.S. discoveries of the mcr-1 gene in the patient and the pig are both troubling:

The discovery in human sample from Pennsylvania is troubling because the mcr-1 gene is on a shareable piece of DNA, which also carries seven other genes that confer resistance to other antibiotics. The use of antibiotics associated with any of these resistance genes can result in bacteria sharing and spreading all eight resistance traits. This example highlights that antibiotic resistance is a complex problem and simply reducing use of one particular antibiotic isn’t enough. Because of the biology of bacteria and the way that they can collect and share groups of resistance traits, overusing one antibiotic can cause collateral damage, spreading resistance to other antibiotics that weren’t used in the first place.

The patient from Pennsylvania hadn’t been traveling in the past few months, so scientists are unsure where she picked up the colistin-resistant E. coli, but it’s likely the bug has been in the U.S. for a little while. Since bacteria don’t stay put, it’s also very likely that the colistin-resistant E. coli has also already moved on to other communities, animals, and people.

The discovery in the pig is troubling for different reasons.  The mcr-1 gene was found in a pig intestine sample that was collected through NARMS (National Antimicrobial Resistance Monitoring System), a program that tests resistance in bacteria from animals, people, and retail meat. Because NARMS only samples a few hundred of all the hogs slaughtered in the U.S. (100 million in 2014), the fact that we have detected the mcr-1 gene in swine at all means that it’s not likely to be at low levels. As with the human sample, the colistin-resistance in the pig sample is also grouped with other resistance genes on a shareable piece of DNA, allowing colistin resistance to be spread because of the use of antibiotics other than colistin.

Both discoveries underscore why curbing antibiotic use in livestock production is critical to keeping our life-saving antibiotics, like colistin, working when we need them.

More than 70 percent of antibiotics important for human medicine sold in the U.S. are actually sold for use in livestock—often for routine growth promotion and disease prevention in animals that are not sick. To change that, we need action from our government leaders and the food industry.

The Obama administration’s new National Action Plan to Combat Antibiotic Resistant Bacteria sets a target for reduction of human use of antibiotics and for data collection and reporting on antibiotic use in hospitals and outpatient setting. This year hospitals in the U.S. have begun to report their antibiotic use to the CDC in an attempt to gather more information and best target education efforts to those overprescribing. Yet, nothing close to these objectives is being attempted to track antibiotic use in animal agriculture, where the vast majority of these antibiotics are being used. FDA and USDA should set targets for reducing agricultural antibiotic use and must stop dragging their feet on collecting better data on such antibiotic use to inform action to protect public health.

In the absence of federal action, NRDC and our allies have focused on advancing change through state policy and the marketplace.

Last year, California enacted a first-in-the nation law, which bans the regular use of antibiotics in livestock and requires the state to collect data on antibiotic use on farms.

In the marketplace, NRDC and others have been waging successful efforts to encourage the meat and restaurant industries to adopt better antibiotics policies. As a result, fast food giants like McDonald’s, Subway, Chick-Fil-A and Taco Bell—as well as some of the nation’s largest chicken producers like Tyson, Perdue and Foster Farms—have committed to improving their antibiotics practices.

Leading public health authorities like the CDC and World Health Organization are clear: If we don’t stop abusing antibiotics, we will continue to see them fail when we need them most. Today’s news is a sobering signal that that reality is closer than many may realize, and there’s no time to delay. We need both industry and our leaders in Washington to take swift action to ensure we can continue to rely on our miracle drugs.

About the Authors

Carmen Cordova

Staff Scientist, Food & Agriculture program

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