Ampicillin resistance was defined as a minimum inhibitory concentration (MIC) greater than 16 g/mL.

What causes resistance to ampicillin?

An OXA-1 β -lactamase, located in an integron, was responsible for resistance to ampicillin.

Why is ampicillin resistance gene necessary?

Adding an antibiotic resistance gene to the plasmid solves both problems at once – it allows a scientist to easily detect plasmid-containing bacteria when the cells are grown on selective media, and provides those bacteria with a pressure to keep your plasmid.