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.

Can bacteria survive an antibiotic that once killed them? This two-part project uses E. coli to explore that question. You streak it across an agar plate, then place disks of penicillin G and tetracycline on the surface. After incubation, a clear zone forms around each disk where the drug stopped bacterial growth. The size of that zone reveals whether E. coli is sensitive or resistant to each antibiotic — a direct measure of how this well-studied bacterium responds to repeated drug exposure.

When germs change so that medicines no longer kill them, you can detect that shift by testing whether an antibiotic still works. In this experiment, disks of penicillin G and tetracycline are placed on an E. coli plate and incubated. The clear zone around each disk reveals the result: a large zone means the bacteria are sensitive, while a small or missing zone signals the medicine no longer works against them.

Antibiotics kill harmful bacteria or stop them from growing, but repeated exposure can leave some bacteria alive — and those survivors keep growing anyway. This two-part project tests that dynamic directly. First, you press everyday objects onto agar plates, one containing an antibiotic in the medium, and compare growth after a week. Then you streak E. coli across a fresh plate and place disks of penicillin G and tetracycline on it. After incubation, the clear zone around each disk reveals whether E. coli is sensitive or resistant to that antibiotic.