The US has reported its first case of a patient with a bug resistant to the antibiotic colistin, known as the drug of last resort.
The 49-year-old woman in Pennsylvania has recovered from her illness, but US health officials warned of the risk of the case representing "the end of the road" for antibiotics.
Dr Tom Frieden, director of the Centers for Disease Control and Prevention, told reporters in Washington: "It is the end of the road for antibiotics unless we act urgently. We risk being in a post-antibiotic world."
In the UK in December, Public Health England reported that it had tested samples and also found resistance to colistin.
If bugs develop the colistin-resistance gene, doctors may be out of treatment options.
UK health officials have repeatedly warned doctors not to prescribe antibiotics unless absolutely necessary.