“What kept us out of trouble for the last 60 years is that every time drug resistance caught up to us, the pharmaceutical companies would go back to the drawing board and develop the next generation of drugs to keep us ahead of the game,” said Brad Spellberg, an infectious diseases physician in Los Angeles who heads a microbial resistance task force for the Infectious Diseases Society of America. “That’s the part of the equation that’s changed. Drug companies are no longer trying to get one step ahead.”

Experts point to three reasons pharmaceutical companies have pulled back from antibiotics despite two decades of screaming alarms from the public health community: There is not much money in it; inventing new antibiotics is technically challenging; and, in light of drug safety concerns, the FDA has made it difficult for companies to get new antibiotics approved.

As a result, only four of the world’s 12 largest pharmaceutical companies are researching new antibiotics, said David Shlaes, a drug development veteran and consultant.