Almost all of our antibiotics are designed to kill growing bacteria. If the bacteria don’t grow, they don’t die. Think of the microbes as bicycles and antibiotics as sticks. If a bicycle’s wheels are turning, a well-placed stick can do catastrophic damage. If the wheels are still, the stick passes harmlessly through. This strategy for beating antibiotics is called tolerance or persistence or dormancy. It has many names but a common theme: keep your head down, wait for danger to pass, and start growing again.

That’s exactly what the common gut bacteria Escherichia coli did when Ofer Fridman from the Hebrew University in Jerusalem exposed them to the antibiotic ampicillin. Even though he used very high doses, around 1