Ampicillin: Difference between revisions
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==Mechanism of Resistance== | ==Mechanism of Resistance== | ||
Expression of [[β-lactamase]] neutralizes ampicillin. When this enzyme is expressed on a high-copy number plasmid there is significant diffusion into the extracellular medium. As a result non-resistant satellite colonies may form around larger resistant colonies. | Expression of [[β-lactamase]] neutralizes ampicillin. When this enzyme is expressed on a high-copy number plasmid there is significant diffusion into the extracellular medium. As a result non-resistant satellite colonies may form around larger resistant colonies. | ||
[[Image:Amp2.jpg|thumb|300px|left|Satellite colonies on an Ampicillin plate]] | |||
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==Usage Notes== | ==Usage Notes== | ||
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The authors reccommend not allowing cultures to reach stationary phase if you need a high proportion of cells to contain your plasmid. | The authors reccommend not allowing cultures to reach stationary phase if you need a high proportion of cells to contain your plasmid. | ||
==References== | ==References== | ||
Molecular Cloning: A Laboratory Manual, Vol 1. | Molecular Cloning: A Laboratory Manual, Vol 1. | ||
Revision as of 14:30, 3 November 2005
Mode of Action
Inhibits the formation of cross-links in the peptidoglycan layer (which prvides rigidity to the cell wall). Most effctive against cells in log phase growth (since this is when new cross-links are being formed), and has little effect on cells in stationary phase.
Mechanism of Resistance
Expression of β-lactamase neutralizes ampicillin. When this enzyme is expressed on a high-copy number plasmid there is significant diffusion into the extracellular medium. As a result non-resistant satellite colonies may form around larger resistant colonies.
Usage Notes
A 1990 paper by Bill Studier discusses how the secreted β-lactamase can quickly consume all the ampicillin in a culture (even at 20μg/ml Amp). A stationary culture of ampicillin resistant cells can have such a concentration of β-lactamase that even a 1/200 to 1/1000 dilution will still contain enough β-lactamase to consume all the fresh ampicillin before all the non-resistant cells from the stationary phase culture have been killed.
The authors reccommend not allowing cultures to reach stationary phase if you need a high proportion of cells to contain your plasmid.
References
Molecular Cloning: A Laboratory Manual, Vol 1.
