a Petri plates with a plastic divider create two chambers. The left chamber is poured with media without antibiotic, and the right chamber with antibiotic. After the media is set, the two chambers are connected by a thin layer of agar on the top of the bridge12. Bacteria are inoculated in the left chamber as indicated, and allowed to swarm to the right chamber. b As in (a), but with dead bacteria layered on the surface of media on right.