Structures made of DNA are designed to target the bacteria that cause cholera.

A bioengineered molecular ‘grenade’ unleashes a poison when ingested by specific bacteria, offering scientists a potential method for killing pathogens without harming beneficial microbes.

Bacterial cells often contain plasmids, ring-shaped structures made of DNA. Didier Mazel at the Pasteur Institute in Paris and his colleagues created plasmids that carry the genetic blueprint for an anti-bacterial toxin. The plasmids also carry genes that serve as switches. These switches allow toxin to be produced only after the plasmids are nestled inside antibiotic-resistant Vibrio cholerae, the bacterium that causes cholera. The researchers then loaded these plasmid ‘weapons’ into donor bacteria, which transferred them to V. cholerae cells.

The plasmids killed 100% of antibiotic-resistant cholera bacteria in a lab sample. They also killed cholera bacteria that had infected brine shrimp (Artemia nauplii) and zebrafish (Danio rerio) — but left the harmless bacteria in the animals’ microbiomes unscathed.

The plasmids’ genetic switches can be customized to direct the poisonous grenades to detonate inside a wide range of pathogens, the authors write.

For a News & Views on this story, see https://www.nature.com/articles/d41586-019-01852-w