Antibiotic Selection

Antibiotic selection is a method used to identify bacterial cells that have taken up a plasmid.

A plasmid is a small circular DNA molecule that includes a gene of interest for expression in host cells, along with an antibiotic resistance gene that provides resistance to specific antibiotics.

During transformation, plasmid DNA and bacterial cells are incubated together. A heat shock step is then performed, causing some cells to take up the plasmid, while many cells do not receive the DNA.

After a brief recovery period, the cells are plated onto a medium containing the selected antibiotic.

Transformed cells with the resistance gene produce proteins that break down the antibiotic or block its effects. This allows the cells to survive and grow.

Non-transformed cells do not contain the resistance gene, so they cannot survive on the antibiotic-containing medium.

Because the resistance gene and the gene of interest are located on the same plasmid, the surviving cells usually also contain the gene of interest.

Following antibiotic selection, only transformed cells carrying the recombinant plasmid survive and form visible bacterial colonies on the plate.

After selection, scientists pick these colonies and screen them using methods such as colony PCR, restriction digestion, or DNA sequencing to confirm the presence of the gene of interest.