New tactics in controlling infection are sorely needed, with antibiotic-resistant bacteria expected to claim as many as 2 million lives each year by 2050.

US and Spanish researchers have now discovered at least some bacteria pay a steep price for their resistance – a cost that we may be able to exploit to fight infection.

"We discovered an Achilles heel of antibiotic-resistant bacteria," says molecular biologist Gürol Süel from the University of California, San Diego.

"We can take advantage of this cost to suppress the establishment of antibiotic resistance without drugs or harmful chemicals."

Exploring why bacteria with resistance factors don't necessarily dominate their non-resistant relatives, University of California, San Diego biologist Eun Chae Moon and colleagues discovered an example of protection that comes at a cost, impeding the bacteria's ability to survive when levels of magnesium are low.