Written and maintained by CASRAI Editorial Board
Last updated
Short answer
A plasmid antibiotic resistance gene is a gene carried on a plasmid that lets the bacterium holding it survive an antibiotic. The same kind of plasmid does two jobs. In a clinical or environmental setting, resistance plasmids are vehicles that capture and spread resistance genes between bacteria. In a research lab, an antibiotic resistance gene on a cloning plasmid is a deliberate selection marker that shows which bacteria took the plasmid up.
Definition and scope
A plasmid is a separate DNA molecule that a bacterium can carry alongside its chromosome (see plasmid vector and plasmid design for the lab-construct side). An antibiotic resistance plasmid, also searched as a plasmid antibiotic resistance or antibiotic resistance plasmid, is one that carries a gene giving its host resistance to one or more antibiotics.
Bennett’s 2008 review in the British Journal of Pharmacology states that plasmids “serve a central role, as the vehicles for resistance gene capture” and their dissemination. The review places this against antibiotics having been in clinical use for “a little more than 6 decades” and names transposable elements and integron systems as other gene-transfer systems involved in resistance.
This page covers the concept and its laboratory relevance. It does not give clinical guidance, and it does not repeat bench concentrations that already have their own page, such as ampicillin working concentration.
How resistance genes spread between bacteria
The CDC explains that antibiotic use pressures bacteria to adapt, and that “These surviving germs have resistance traits in their DNA that can spread to other germs.” Germs can also share their resistance mechanisms with other germs that have not been exposed to antibiotics or antifungals. The CDC page does not discuss plasmids by name; the plasmid-specific statement here comes from the review literature.
Bennett describes plasmids as vehicles for resistance gene capture and goes as far as saying that “the genomes of all bacteria can be considered as a single global gene pool.”
What resistance can look like inside the cell
The CDC lists five ways germs resist drugs:
- restrict access of the antibiotic, so the drug cannot get in
- get rid of the antibiotic, for example with pumps
- change or destroy the antibiotic, for example with enzymes
- change the target the antibiotic acts on
- bypass the effects of the antibiotic
These are general mechanisms of antimicrobial resistance as described by the CDC, not a list of what any particular plasmid gene does.
Resistance genes as selection markers in the lab
Addgene explains that a resistance gene on a plasmid allows “for selection of plasmid-containing bacteria by providing a survival advantage to the bacterial host.” The gene is under the control of a bacterial promoter, so it is expressed in bacteria. Bacteria that took up the plasmid grow on antibiotic-containing medium; those that did not are held back. This is the step that makes bacterial transformation workable, and it depends on starting with competent cells.
Addgene’s advice for choosing the antibiotic is to check your plasmid’s datasheet or the plasmid map. Reading that map is covered in how to read a plasmid map.
Selection antibiotics at a glance
Addgene’s antibiotics reference lists these recommended stock and working concentrations. Use the values on your own plasmid’s datasheet where they differ.
| Antibiotic | Stock (mg/mL) | Working (µg/mL) |
|---|---|---|
| Ampicillin | 100 | 100 |
| Carbenicillin | 100 | 100 |
| Chloramphenicol | 25 (dissolve in ethanol) | 25 |
| Hygromycin B | 200 | 200 |
| Kanamycin | 50 | 50 |
| Spectinomycin | 50 | 50 |
| Tetracycline | 10 | 10 |
Addgene notes that carbenicillin can be used in place of ampicillin.
Where it matters for labs and supply decisions
- Know which antibiotic your plasmid needs before preparing media. Addgene points to the plasmid datasheet or map as the place to find it.
- Treat the marker as a real resistance trait. The CDC notes that resistance traits in DNA can spread to other germs. Follow your institution’s biosafety rules for handling and disposal of these cultures.
- Match the antibiotic to the selection you intend. Addgene lists carbenicillin as usable in place of ampicillin; the other antibiotics in the table are separate selections.
- Record which stock and working values your lab used.
Common misunderstandings
- “A selection marker is not a real resistance gene.” It provides a survival advantage to the bacterial host, as Addgene puts it, which is what resistance means in practice.
- “Resistance only arises in bacteria that met the drug.” The CDC states that germs can share resistance mechanisms with germs that have not been exposed to antibiotics.
FAQ
What is an antibiotic resistance plasmid?
A plasmid that carries a gene giving its bacterial host resistance to one or more antibiotics. Bennett’s review describes plasmids as vehicles for resistance gene capture and dissemination.
Why do cloning plasmids carry an antibiotic resistance gene?
According to Addgene, it allows selection of plasmid-containing bacteria by providing a survival advantage to the bacterial host.
How do I know which antibiotic to use?
Addgene advises checking your plasmid’s datasheet or the plasmid map.
Can carbenicillin replace ampicillin?
Addgene’s reference notes that carbenicillin can be used in place of ampicillin.
Does the CDC say plasmids spread resistance?
The CDC page on antimicrobial resistance says resistance traits in DNA can spread to other germs, but it does not mention plasmids by name.
Sources
All sources checked 2026-10-29.
- Bennett PM. Plasmid encoded antibiotic resistance: acquisition and transfer of antibiotic resistance genes in bacteria. Br J Pharmacol. 2008. https://pubmed.ncbi.nlm.nih.gov/18193080/
- Centers for Disease Control and Prevention. About Antimicrobial Resistance. https://www.cdc.gov/antimicrobial-resistance/about/index.html
- Addgene. Antibiotics (molecular biology reference). https://www.addgene.org/mol-bio-reference/antibiotics/
