Antibiotic-containing paper disks are then applied to the agar and the plate is incubated. If an antibiotic stops the bacteria from growing or kills the bacteria, there will be an area around the disk where the bacteria have not grown enough to be visible. This is called a zone of inhibition.
Antibiotic-containing discs are applied to agar plates, and if an antibiotic halts bacterial growth or kills bacteria, a zone of inhibition will form around the disc where the bacteria haven't grown enough to be visible. This is called a zone of inhibition.