Even when not threatened, some bacteria specialize as antibiotic resistance"It's costly from a metabolic standpoint for a cell to express the proteins that enable it to be resistant," said Mary Dunlop, assistant professor in the university's College of Engineering and Mathematics Sciences, and the paper's corresponding author. "This strategy allows a colony to hedge its bets by enabling individual cells within a population to assume high levels of resistance while others avoid this extra work." Previous research has demonstrated that, when exposed to some antibiotics, all the cells within a bacterial population will use the protein cascade strategy, activated by a mechanism called MarA, to become resistant. But the new study is among the first to show that colonies use the protein cascade strategy even when they are not under threat. "This transient resistance, distributed in varying degrees among individual cells in a population, may be the norm for many bacterial populations," Dunlop said.