In article <5n6ba2$nqk at info.abdn.ac.uk>, mbi071 at sysc.abdn.ac.uk says...
>I've found that simply growing them in LB 2x overnight
>cultures without antibiotic selection has done the trick without any
>nasties. I just plated out, picked 100 colonies and replica plated them
>on LB and LB Amp, about 20% had lost the plasmid.
This is exactly what I do, and it works great!