Escherichia coli bacterium.

The bacterium Escherichia coli is vulnerable to a new antibiotic that responds to visible light. Credit: Steve Gschmeissner/SPL/Getty

Chemistry

Drug delivery with the flip of a light switch

Turn it on, turn it off — a new antibiotic responds to visible light.

A common medication has been converted into the first antibiotic to employ visible light as an on–off switch.

A drug that can be easily turned on and off could provide targeted treatment, and the ability to deactivate antibiotics could help to battle drug resistance. But previous efforts to develop light-sensitive antibiotics produced compounds controlled by ultraviolet (UV) light, which kills healthy cells.

Wiktor Szymański and Ben Feringa of the University of Groningen in the Netherlands and their colleagues wanted to make an antibiotic that could be activated by visible light, which is more benign. The researchers took the core structure of an antibiotic called trimethoprim and added chemical groups that act as ‘photoswitches’ at various positions; this initially created a compound responsive to UV light and active against the pathogen Escherichia coli.

When the team added chlorine to the photoswitch, the resulting antibiotic could be switched on with red light, making it eight times more potent against bacteria when on than off.