Shelf life of ampicillin in LB media? - (Mar/10/2009 )

we generally streak in ampicillin plate and keep it in incubator for overnight ie 15 hrs.does ampicillin degrade in the plate within that period of time?

sagar on Mar 10 2009, 10:18 AM said:

hi sagar,
i am pretty sure ampicillin plates do not degrade overnight...for that reason we can effeciently carry out transformation.well things do not turn up good all the time. I can safely comment that it does not get degraded overnight.

Amp should be stable overnight at 37 oC . However, colonies of resistant bugs can secrete beta-lactamase into the agar medium. Thus there will be an area around a resistant colony with little, if any, active amp. This can often be seen on transformation plates as small satellite colonies of non-resistant bugs circling a large resistant colony.

klinmed on Mar 10 2009, 10:44 AM said:

ya thats a nice answer to that. good

klinmed on Mar 11 2009, 12:14 AM said:

yah thanks.
logic is good.may be for that reason we get sometimes false colonies.

Hi!

I kept my Amp plates for almost 1 month at 4°C and they stayed selective. Also incubation for more then 2 days at 30°C did not influence selectivity so the antibiotic should be ok. Some papers say that you should not keep these plates for more than one week but from my experience they still work if you store them at 4°C. Good luck!

As for me, I make new plates once in a few months and store them at -4C - and when I finally use it, Amp works perfectly. Never had a single problem with that.
I observed these little sattelite colonies klinmed had mentioned before, but it took them about a week to grow. One night at 37C is safe.
If you actually have troubles with selectivity, than perhapse you should increase Amp concentration.