For the first time, researchers have found a person in the United States carrying a bacteria resistant to antibiotics of last resort, an alarming development that the top US public health official says could mean "the end of the road" for antibiotics.

The antibiotic-resistant strain was found last month in the urine of a 49-year-old woman in the US state of Pennsylvania. Department of Defence researchers determined that carried a strain of E. coli resistant to the antibiotic colistin, according to a study published on Thursday. The authors wrote that the discovery "heralds the emergence of a truly pan-drug resistant bacteria."

Colistin is the antibiotic of last resort for particularly dangerous types of superbugs, including a family of bacteria known as CRE, which health officials have dubbed "nightmare bacteria." In some instances, these superbugs kill up to 50 per cent of patients who become infected. The Centers for Disease Control and Prevention has called CRE among the country's most urgent public health threats.

The results were published in Antimicrobial Agents and Chemotherapy, a publication of the American Society for Microbiology.