Chen Ho An
chen at bsm.bioc.ucl.ac.uk
Tue Aug 11 08:12:15 EST 1998
Koichi Kunitake (kunitake at salk.edu) wrote:
: Maybe the amp kills only growing bacteria, and perhaps the one
: bacterium that had the amp resistance made the B-lactamase while it was on
: the LB-amp plate, so there was no need to incubate at 37C beforehand.
: Do people routinely incubate at 37 for an hour before plating out? it
: seems like it isn't necessary, at least for ampicillin, and I would be
: curious to know if people have tried it with other antibiotics.
No need to try it with other antibiotics. If you know how each antibiotic
work, then you won't need to ask this question. Ampicilin affects the
synthesis of cell wall, causing cell lysis in growing and dividing cells.
If the cell is not expanding or dividing, it is unaffected by ampicillin.
The cell can have the time to express beta-lactamase which can then
inactivates ampicillin, therefore there's no need for recovery time for
the beta-lactamase to be expressed (anecdotally some have even suggested
it is better not to incubate).
However, for other antibiotics like chloramphenicol or tetracyline which
affect the synthesis of protein, you must incubate the cells, otherwise
your gene product will not be expressed and therefore there is no
protection against the antibiotics.
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