How big is the clear ring? That depends on the treatment. Disks soaked in acne medications go onto agar plates covered with P. acnes bacteria, and after incubation you measure the ring where bacteria could not grow. Comparing ring sizes reveals which treatments are strongest — prescription antibiotics produced the largest ones, but oregano oil turned up as a surprise third-place finisher.

You soak paper disks in three soaps and place each one on a bacteria-covered plate. After a day in the incubator, the clear ring around each disk — where no germs could grow — tells you how well each soap performed. Tracking those rings over seven days shows whether the effect holds steady or fades with time.

A shrinking clear ring can be an early warning. In this project, disks of penicillin G and tetracycline go on an E. coli plate. The size of each ring shows whether E. coli is sensitive or resistant to that antibiotic — a large clear zone means the drug works, while a tiny one, or none at all, means the bacteria can fight it off.

You swab your mouth to isolate alpha streptococcus, grow it on Mueller Hinton plates, then apply measured doses of different mouthwashes. After overnight incubation, the clear ring around each sample — where bacteria stopped growing — gives you a direct readout of effectiveness. The wider the ring, the harder that mouthwash hit the bacteria.

Do antibacterial soaps actually outperform regular ones? Discs soaked in both types go on plates with three bacterial species, and the clear ring around each disc — where bacteria could not grow — gives a concrete answer. Comparing those rings across bacterial species tells you whether the antibacterial ingredient makes any real difference.