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Plasmid-Reference_book.png Antibiotic Concentrations for Bacterial Selection


Background Information

Plasmids carry antibiotic resistance genes, which confer antibiotic resistance to the bacteria carrying them. The presence of these antibiotic resistance genes on plasmids allows researchers to easily isolate bacteria containing the plasmids from those that do not by artificial selection (i.e. growing them on or in a medium containing the antibiotic).

You should check your plasmid's datasheet or the plasmid map to determine which antibiotic to add to your LB media or LB agar plates.

Preparing Antibiotics

  1. Create a stock solution of your antibiotic. Addgene recommends making 1000X stock solutions and storing aliquots at -20°C.

    Antibiotic Concentrations:

    Antibiotic Recommended Stock Concentration Recommended Working Concentration
    Ampicillin 100 mg/mL 100 µg/mL
    Bleocin 5 mg/mL 5 µg/mL
    Carbenicillin* 100 mg/mL 100 µg/mL
    Chloramphenicol 25 mg/mL
    (dissolve in EtOH)
    25 µg/mL
    Coumermycin 25 mg/mL
    (dissolve in DMSO)
    25 µg/mL
    Gentamycin 10 mg/mL 10 µg/mL
    Kanamycin 50 mg/mL 50 µg/mL
    Spectinomycin 50 mg/mL 50 µg/mL
    Tetracycline 10 mg/mL 10 µg/mL

    Note: Unless otherwise indicated, the antibiotic powder can be dissolved in dH20.

    *Note: Carbenicillin can be used in place of ampicillin. Carbenicillin is more stable, so it is potentially more effective at selecting only bacteria containing the plasmids of interest (for example, fewer satellite colonies will grow). However, it is also more expensive.

  2. To use, dilute your antibiotic into your LB medium at 1:1,000. For example, to make 100 mL of LB/ampicillin growth media, add 100 μL of a 100 mg/mL ampicillin stock (1000X stock) to 100 mL of LB.