Today I learned that you should immediately plate bacteria that have ampicillin, and that it is SOP to do so in our lab here at Olin. It doesn’t matter that you add them immediately, because they have time to inactivate the amp before they divide, which is when the amp kills them. Maybe this explains all the satellite colonies I saw before! I was waiting a good 15-30 minutes, which allows the bacteria to express beta-lactamase, which breaks down ampicillin. This can destroy nearby ampicillin on the surface of plates, destroying any antibiotic effect, creating satellite colonies. Oops. Time to revisit my transformation protocol.