Kim Lewis, who has made several major discoveries in the fight against bacterial infections, has been named a Fellow of the American Association for the Advancement of Science.

 Lewis, who is the director of Northeastern’s Antimicrobial Discovery Center and a University Distinguished Professor of Biology, has spent his 16 years at the university collecting scientific paradoxes and tackling them in his lab. Why can’t certain bacteria be grown in a petri dish? Why does Lyme disease seem to linger in some patients?

“One of the paradoxes on my list was this paradox of chronic infections,” said Lewis, who is also a Fellow of the American Academy of Microbiology. “Why drug-susceptible bacteria cannot be eradicated by an antibiotic that kills them on a petri dish.”

Lewis discovered the answer: bacterial persister cells.

In a chronic infection, the bacteria typically form a biofilm—a mass of cells that stick together with a sort of slimy goo. When those infections are treated by antibiotics, a small population of cells survives to repopulate. Most researchers thought that these bacteria were evolving resistance to the antibiotic.

“Early on, I made a guess that resistance had nothing to do with it,” Lewis said.

Instead, Lewis found, a small subpopulation of the bacterial cells are entering a semi-dormant state. They shut down the pathways that antibiotics target, making them temporarily tolerant. Those cells survive the antibiotic onslaught, then come out of their dormant state to regrow the infection.

Lewis’s lab has continued to study bacterial tolerance, investigating the mechanisms that cause persisters to form and searching for ways to combat them. One of their discoveries has been licensed to a Boston-based biotech startup, hopefully to be made into a drug that will help kill off persisters and eliminate chronic infections.

Lewis was nominated by his colleagues at the American Association for the Advancement of Science, the largest multidisciplinary scientific society in the world, for his discovery and understanding of persister cells.

“My grad student at the time, Amy Spoering, asked me, ‘So what did we discover? What is our contribution to the field?’ I said, ‘Well, you and I closed an important field of science,’” Lewis said. “We closed that field and opened another one: the study of tolerance.”