how long is carb stable in liquid broth at 37C - I need longer incubation times of bacteria because of the transformant (Dec/18/2009 )

Hi all,
I have transformed E.coli with a transformant which makes them grow slower compared to normal E.coli (I've seen that in agar plates). Because of this, the doubling times are increased. So when I want to make miniprep, I have to let them grow longer times (like 24-36 hrs at 37C). Here is my question: is carbenicillin stable in the broth at 37C for such a long time? I am concerned if the things which grow after 36 hrs might be contaminants.
Thanks in advance for your help!

Check the pH of your broth after 24 hrs, if it is not acidic, then carb should be stable... I am guessing you are using LB @ 7.4.