Weeks after federal researchers confirmed the first discovery in the U.S. of a particular gene plasmid that can make bacteria resistant to an important antibiotic of last resort, a new report has turned up a second stateside instance of the gene.

The MCR-1 gene can make bacteria resistant to colistin, an antibiotic that is both incredibly powerful and potentially toxic. Colistin went largely unused for decades until the recent increase in drug-resistant antibiotics required its use in some patients.

The existence of MCR-1 was first reported in Nov. 2015, and at the time is was believed that the gene was “confined to China.”

However, by Jan. 2016, researchers had found MCR-1 in 19 different countries on four continents, but not in the U.S.

In a report released today in the journal Antimicrobial Agents and Chemotherapy, researchers from JMI Laboratories in Iowa say their analysis of colistin-resistant E. coli samples from around the world turned up 19 instances of MCR-1, including one case in the U.S.

This U.S. sample is actually from 2015, meaning it predates the case — involving a Pennsylvania woman — confirmed in April by the Walter Reed National Military Medical Center.

While the MCR-1 gene conferred colistin resistance to the bacteria in both cases, the E. coli in the JMI Labs report was susceptible to several less-toxic antibiotics. The bacteria found in the Walter Reed case was really only sensitive to carbapenems, antibiotics used for the treatment of multi-drug resistant pathogens.

The JMI Labs report notes that the bacteria containing the MCR-1 gene came from a variety of infection types. Of the 19 positive samples, eight came from bloodstream infections, five from skin and skin structure infections, three from urinary tract infections, two from respiratory tract infections, and one intra-abdominal infection.

The 19 MCR-1 instances in this report come from all over the globe. Samples from Germany turned up five instances of the gene, followed by Italy with four, and Spain with three. Like the U.S., samples from Belgium, Brazil, Hong Kong, Malaysia, Poland, and Russia each turned up a single instance.

One of the biggest concerns about MCR-1 is that it’s not part of the bacteria’s genome. Instead, it’s a plasmid, which means there’s the possibility it could be transmitted between different bacterial species, spreading its resistance.

The overuse of antibiotics — everything from doctors who prescribe the drugs to patients who don’t need them to farmers who put antibiotics in animal feed for growth-promotion — has helped to create drug-resistant bacteria that can’t be treated with traditional antimicrobials.

At the same time, the government and the pharmaceuticals industry has not developed new antibiotics. According to a recent report from the Pew Charitable Trusts, no new types of antibiotics have been discovered in more than 30 years, raising the concern that resistance — in the absence of new drugs — could wipe out the utility of the ones we’ve been using since the golden ages of antibiotics research in the mid-Twentieth Century.

In the wake of the Walter Reed MCR-1 discovery, federal lawmakers renewed their push for the Promise for Antibiotics and Therapeutics for Health (PATH) Act, which would create an expedited process for the development and approval of certain antibiotics to treat life-threatening infections in limited populations.

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