Antibiotic resistance happens when bacteria gain the ability to survive a drug that once killed them — and one way to study that is by introducing the trait directly. In this experiment, you add foreign DNA in the form of a pGLO plasmid to E. coli. That plasmid carries two genes: one that makes the bacteria resistant to ampicillin, and one that produces a fluorescent protein activated by arabinose sugar. After mixing E. coli with cold calcium chloride and the plasmid DNA, you heat-shock the cells at 42 degrees Celsius for 50 seconds, then spread them onto agar plates containing ampicillin and arabinose. The hypothesis predicts the bacteria will be transformed into an ampicillin-resistant strain — and transformed colonies, viewed under a UV lamp, will glow.

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.

Why do antibiotics sometimes stop working? When bacteria survive a dose, the survivors pass their resistance to the next generation. This experiment spreads E. coli on agar plates and places filter paper discs soaked in ampicillin at 1 mg, 3 mg, and 5 mg. After each round, you measure the inhibition zone — the clear ring where no bacteria grow — then collect survivors from the edge and repeat. Over five generations, the zones shrink. The 1 mg zone drops from 24 mm to 11.5 mm, showing the bacteria have changed enough that the medicine now works far less effectively.