Bacteria often coordinate efforts chemically with their neighbors using a process called quorum sensing. The microbes release molecules that they all recognize as signals for common activities such as forming a biofilm or releasing toxic virulence factors to attack a host. A study has now found that a compound made by plants, rosmarinic acid, can mimic the actions of a common class of quorum-sensing molecules (Sci. Signaling 2016, DOI: 10.1126/scisignal.aaa8271). Plants may use rosmarinic acid to protect themselves against infections by butting into bacterial conversations, a strategy scientists could adopt in the design of new antimicrobial drugs. Through computational modeling and microcalorimetry experiments, Tino Krell of the Spanish National Research Council and colleagues found that rosmarinic acid can bind to a known quorum-sensing regulator protein used by the pathogenic bacteria Pseudomonas aeruginosa. The compound is more potent than the bacteria’s own quorum-sensing molecule, a homoserine lactone, binding tighter to the regulator and stimulating greater levels of gene expression. The researchers think rosmarinic acid makes bacteria vulnerable by forcing them to jump the gun on a sensing response before they have sufficient numbers to reach a quorum.