Kirby-Bauer antibiotic testing (KB testing or isk diffusion antibiotic sensitivity testing) is a test which uses antibiotic-impregnated wafers to test whether particular bacteria are susceptible to specific antibiotics. A known quantity of bacteria are grown on agar plates in the presence of thin wafers containing relevant antibiotics such as trimethoprim and nitrofurantoin, commonly used to tackle urinary tract infections. If the bacteria are susceptible to the antibiotics, an area of clearing surrounds the wafer where bacteria are not capable of growing (called a zone of inhibition, or the clear zone).