There are two scenarios with this post Kim, for which I will try and advise you:
1.If you are visiting a breeder, I personally would collect my food and leave. I would not touch any bunnies, that could potentially have disease, and then take it back to my own. If they are irresponsible enough not to seek vet care, then thats up to them, but you need to ensure that you are not walking in a contagious disease to your own.
2. If your own bunnies are still unwell following the vet diagnosing the E Coli, I would take them back to the vet and ask him if he feels the bunnies could have mucoid enteritis. The sooner they start on treatment for this, if this is likely, the better.