Why does a plasmid contain an antibiotics resistance gene?

Additionally, the presence of a plasmid is disadventageous from the bacterium's perspective – a plasmid-containing cell must replicate the plasmid in addition to its own chromosomal DNA, costing additional resources to maintain the plasmid. read more

The plasmid is too small to be seen, so it is useful for it to contain a gene that express a characteristic than can be seen or interpreted, for example, antibiotic resistance. As a result, only bacteria containing a plasmid with antibiotic resistance will grow in the presence of antibiotic ampicillin. read more

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. read more