Touching poop while changing diapers. couldn't this give him e.coli infection?

Not likely.: If it is touched while changing, it is likely his e. Coli, so he won't likely get infected, but you should wash your hands so you don't get sick, and keep him/her/baby clean there, so bacteria doesn't build up, or infection can result from too much/ too many kinds of bacteria. So wash the baby thoroughly when changing, and wash your hands before and after changing to be sure.

Some basics: There is E.coli in all poop. There are E.coli good (benign, common) and E.coli bad (cause a variety of problems, infections, kidney failure, etc.). It is important to try to avoid soiling and wash after the process, but I would not assume than any breach in technique will make anyone involved sick on every occasion.