Antibiotic stocks and dilutions
How much stock to add to a culture, and what to weigh to make the stock.
Solvent: Water. Degraded by β-lactamase secreted into the plate, so satellite colonies appear around a resistant one on older plates. Carbenicillin is the more stable substitute.
Stock to add
A 1 in 1000 dilution, delivering 50 mg.
V_stock = C_working × V_culture ÷ C_stock- Working and stock concentrations for bacterial selection — Addgene molecular biology reference
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The reference concentrations are the usual ones for selecting plasmids in E. coli. A low-copy plasmid, a rich medium or a different organism all change them. Add antibiotics to molten agar only once it has cooled to about 50 °C — poured hot, several of them are destroyed before the plate sets.
About this tool
Work out the volume of an antibiotic stock to add to a given volume of medium for a target working concentration, and the mass to weigh out to make the stock in the first place. Carries the usual working and stock concentrations for selecting plasmids in E. coli, with the solvent each needs and what tends to go wrong with it — all editable, because a different organism or a low-copy plasmid changes them.
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Science last reviewed .