The superbug that doctors have been dreading just reached the U.S.

U.S. researchers reported Thursday that a 49-year-old Pennsylvania was recently found to have bacteria resistant to antibiotics of last resort. The researchers, from the Department of Defense, said the woman had a strain of <i>E. coli</i> that is resistant to colistin.

U.S. researchers reported Thursday that a 49-year-old Pennsylvania was recently found to have bacteria resistant to antibiotics of last resort. The researchers, from the Department of Defense, said the woman had a strain of E. coli that is resistant to colistin. In a report in Antimicrobial Agents and Chemotherapy, the researchers wrote that the finding "heralds the emergence of a truly pan-drug resistant bacteria." Colistin is used as an antibiotic of last resort for especially dangerous types of superbugs, including a family of bacteria called carbapenem-resistant enterobacteriaceae (CRE). This is the first instance in which this colistin-resistant strain has been found in a patient in the United States. "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," CDC Director Tom Frieden said Thursday. CDC is now working with health officials in Pennsylvania in an effort to determine how the woman may have contracted the bacteria and to see if others may be carrying the organism.