The U.S. Centers for Disease Control and Prevention (CDC) isn’t known to use hyperbolic language.

Considering its role in combatting potential outbreaks, it’s often reserved with its word choice to avoid creating a panic.

Still, they call carbapenem-resistant Enterobacteriaceae, or CRE, the “nightmare bacteria” for good reason. The strain is resistant to numerous types of antibiotics, making an infection nearly impossible to treat.

It’s deadly in half of those infections.

While many media outlets have reported about a new strain of CRE resistant to powerful antibiotics appearing in the United States, it’s actually E. coli, not CRE. The distinction is important to make, although both are members of the Enterobacteriaceae family.

The real problem isn’t the bug. It’s the gene mcr-1, which makes the bug resistant even to last-ditch antibiotics. And it can quickly pass those genes onto other bacteria.

The threat of this survival resistance spreading to other bugs adds a new level of concern about what options remain to stop these deadly bacteria.

Caring for patients when no drugs work gives doctors “a feeling of such horror and helplessness,” said Dr. Tom Frieden, director of the CDC.

And this new finding highlights a crucial time in modern medicine.

“It basically shows us that the end of the road isn’t very far away for antibiotics — that we may be in a situation where we have patients in our intensive care units, or patients getting urinary-tract infections for which we do not have antibiotics,” he told The Washington Post.

This has infectious disease experts concerned because bacteria across the world are increasingly building defenses against the most powerful antibiotics. And the development of new antibiotics is falling behind.

Every year, according to the CDC’s best estimates, 2 million people are infected with one form of drug resistant bacteria. Of those, 23,000 people die.

Read More: Weakening Antibiotics May Result in 6,300 More Infection-Related Deaths a Year »

The Discovery of mcr-1 in Humans

Researchers have confirmed the strain of E. coli resistant to colistin, a powerful antibiotic discovered in the 1950s. Its use was discontinued in the 1970s because of its toxicity.

The strain was discovered in the United States last month in the urine of a 49-year-old Pennsylvania woman, according to a report released Thursday by researchers at Walter Reed National Military Medical Center. She was being treated for a urinary tract infection, a common source for drug-resistant infections.

These types of drug-resistant urinary tract infections are also on the rise in children, according to recent research.

The woman hadn’t traveled in five months, puzzling researchers where the strain came from.

According to the U.S. Department of Health and Human Services, colistin-resistant E. coli was previously found in a single sample from a pig intestine. The U.S. Department of Agriculture is investigating that pig’s farm of origin.

The potentially deadly bug had been reported in other countries, which to researchers “heralds the emergence of truly pan-drug resistant bacteria.”

Following the initial discovery of the mcr-1 gene and its resistance to colistin in China in November, researchers in Europe and Canada have discovered the bacteria.

While the finding of mcr-1 is alarming, it’s still rare. Experts say none of the more than 44,000 Salmonella and 9,000 E. coli/Shigella samples from several gene databases showed the presence of the mcr-1 gene as of April.

Read More: Chlorine in Water May Be Breeding Drug-Resistant Bacteria »

How Drug Resistance Works

Bacteria follow the mantra, “That which does not kill you only makes you stronger.”

When antibiotics are used but don’t kill the bacteria, they can learn to develop resistance.

Because of this, infectious disease experts have been warning medical officials to use antibiotics judiciously. This includes Alexander Fleming, who discovered penicillin in 1928.

“It is not difficult to make microbes resistant to penicillin in the laboratory by exposing them to concentrations not sufficient to kill them, and the same thing has occasionally happened in the body,” he wrote while accepting the Nobel Prize in 1945. “The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug, make them resistant.”

Routine use of antibiotics — whether by unnecessary prescriptions in humans or administering them to animals in water and feed — gives bacteria more opportunities to develop drug resistance.

Currently in the United States, half of all antibiotic prescriptions for people may be inappropriate. This means they’re given out for conditions where they can only do more harm than good, like the common cold.

Also, the routine administration of antibiotics to livestock has been a concern for decades. Once used for growth promotion, farmers continue to give animals small amounts of antibiotics daily for disease prevention.

All told, estimates by the U.S. Food and Drug Administration show 80 percent of all antibiotics sold in the United States are for animals meant for our dinner plates.

Because of these kinds of misguided uses, Duke University researchers say the rates of drug-resistant E. coli infections have doubled in the past five years.

Read More: How Lethal Bacteria Evolve to Survive »