Bacteria that are immune to every known antibiotic have been reported by hospitals in more than 20 states. Usually hitting those critically ill, they are fatal in 30 to 60 percent of cases.

The bacteria contain a gene that produces an enzyme which immobilizes antibiotics. The enzyme — Klebsiella pneumoniae carbapenamase or KPC — is even effective against carbapenam antibiotics, the drug used to treat infections that don’t respond to other antibiotics.

“We’ve lost our drug of last resort,” Neil Fishman, director of infection control and epidemiology at the University of Pennsylvania, told USA Today.

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