NEW YORK -- For the first time, a U.S. patient has been infected with bacteria resistant to an antibiotic used as a last resort treatment, scientists said Thursday.

The patient -- a 49-year-old woman in Pennsylvania -- has recovered. But health officials fear that if the resistance spreads to other bacteria, the country may soon see supergerms impervious to all known antibiotics.

"It is the end of the road for antibiotics unless we act urgently," Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, said during an appearance in Washington.

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Other countries have already seen multi-drug resistant superbugs that no antibiotic can fight. So far, the United States has not. But this sets the stage for that development, CDC officials said.

The woman had gone to a military clinic in Pennsylvania last month and was treated for a urinary tract infection. Initial tests found she was infected with E. coli bacteria, a common variety of germ seen in the gut that often makes its way to the bladder.

But the tests showed this E. coli was resistant to antibiotics commonly used first for such infections. She was successfully treated with another kind of antibiotic.

But while she has recovered, further testing completed in the last week confirmed that the E. coli was carrying a gene for resistance against the drug colistin.

Colistin is an old antibiotic. By the 1970s, doctors had mostly stopped using it because of its harsh side effects. But it was brought back as other antibiotics began losing their effectiveness.

It's used against hard-to-treat bacteria that resist one of the last lines of defense, antibiotics called carbapenems. If those germs pick up the colistin-resistance gene, doctors may be out of treatment options, health officials say.

"This is another piece of a really nasty puzzle that we didn't want to see here," said Dr. Beth Bell, who oversees CDC's emerging infectious diseases programs.

CBS News medical contributor Dr. David Agus said the case a wake-up call about the growing threat posed by superbugs. "It's a wake-up call for all of us to question whether we need antibiotics, and also for the government to really push these new things in the pipeline to help us," Agus said on "CBS This Morning" Thursday.

The overuse of antibiotics -- and their misuse for viral illnesses like the flu, which don't respond to antibiotics -- have helped drug-resistant strains of bacteria flourish.

The CDC says antibiotic-resistant germs cause more than 2 million illnesses and at least 23,000 deaths each year in the United States. A report out last week from a U.K. government commission warned that unless steps are taken to rein in the problem worldwide, superbugs could claim 10 million lives a year by 2050 -- even more than the current toll from cancer.

Last year the Obama administration announced a five-year plan to combat superbugs and asked Congress to double funding to $1.2 billion, some of which would be spent on efforts to develop a new generation of antibiotics. In an interview with WebMD, President Obama called the spread of drug-resistant superbugs "one of the most pressing public health issues facing the world today."

In this latest case in Pennsylvania, the CDC is working with state health officials to interview the woman and her family to try to figure out how she might have picked up the strain. The woman had not traveled outside of the country recently, officials said.

The colistin-resistant gene has been seen in animals and people in China, Europe and Canada. Federal officials said Thursday that colistin-resistant E. coli has also been found in a pig in the United States, but there was nothing to link the finding to the Pennsylvania case.

Researchers at Walter Reed National Military Medical Center, who did the confirmatory tests, reported on the Pennsylvania case Thursday in a journal of the American Society of Microbiology.