A patient in Pennsylvania is now documented as the first host carrying bacteria resistant to all antibiotics in the United States. The bacteria seems to have been modified by an infection to its own DNA (plasmid) where a gene called mcr-1 made it resistant to even the most powerful antibiotic. Colistin was reserved as the last bastion of antibiotics, reserved for only the most severe infections so as to prevent resistant strains from developing. (Interestingly, WIRED seems to have an unfinished article on Colistin that managed to be indexed by Google.) Although traces of the bacteria have manifested in people in pockets around the globe, this is the first appearance in the United States but its emergence is troubling because the patient had not traveled. The source of the infection is unknown.

[EDIT: A short article on ArsTechnica summarizes the mcr-1 gene and its presence in different strains along with other "last resort" antibiotics that various bacteria have been resistant to.]