Im glad your little Harley is ok. My little Pete had the same bacteria about 6 months ago. All day he was vomiting and had the runs I finally rushed him to the emergency vet in the afternoon when his poo turned black with blood. He needed the same treatment, some iv fluids because he was so dehydrated and antibiotics which almost immediately made him better. My vet told me that this type of bacteria is naturally found in dogs and can just sometimes grow out of hand. Which is strange cause thats not what it sounds like your vet said. I was under the impression Pete already had the bacteria and he may have had some runny poo from something he ate to begin with (which is what the bacteria loves
) when Pete had the bad poo the bacteria released a toxin to promote more diarhea so it could grow more colonys, thus getting out of control. The blood in the stool is caused by the toxin the bacteria releases, it can cause small tears somewhere in the colon which then bleeds. My vet didnt say Pete had gotten the bacteria anywhere she made it sound like something all dogs naturally have so now Im confused, Im going to do some searching and get back to you.