I checked it on Thursday and it didn't appear to have worked. In these cases I usually leave them for a few more hours in the desperate (but often worthwhile) hope some colonies will start to appear. The problem was I forgot and I was then away until Monday. Checked them this morning and found there still wasn't anything - although by that point I'd have probably had a plate singing songs from "Joseph and his technicoloured Germcoat".
My response to this was to repeat the experiment again and to check the gel excision for mygene-GFP had actually worked. Then my
"In that case I've just conclusively shown they can't grow on Ampicillin plates"
I'm deciding to believe that it was the antibiotics that have been in my bloodstream for the last week that was responsible for this work-related antibiotic gaff...