Most of the commonly used plasmid vectors carry at least one antibiotic resistance gene that allows plasmid-containing bacterial cells to survive and multiply in the presence of antibiotics. However, a relatively high concentration of antibiotics can also be lethal even to a plasmid-containing bacterial cell, while low concentration may allow the growth of bacterial cells that do not have plasmid/bacterial cells tend to lose the plasmid. Therefore, an optimized concentration of antibiotics must be added to the culture medium. We have listed some of the commonly used antibiotics and their recommended concentration for the selection and growth of E. coli in the table.
| Antibiotic | Final concentration in bacterial growth medium |
| Ampicillin | 50 – 100 µg/mL |
| Kanamycin | 20 – 50 µg/mL |
| Tetracycline | 10 – 15 µg/mL |
| Chloramphenicol | 25 µg/mL |
| Spectinomycin | 50 µg/mL |
| Carbenicillin | 100 µg/mL |
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