Bacteria called Clostridium Perfringens causing diarrhea!

I have ;posted several threads in the last few days because of diarrhea issues I've been having with my two Shih Tzus, Charlie and Duke.  I finally took a stool sample to the Vet and they tested it and found a bacteria called Clostridium Perfringens.  They said typically it comes from contaminated soil.  Wow, if it's not one thing it's another!  I'm trying to decide if I should send a sample of the soil in our backyard somewhere to have it tested.  I've been feeding them raw food which may or may not be where they got it.  I caught Duke with his face in the grass (the day before he had diarrhea), I picked him up and he had mud on his face and in his mouth.  I don't know what to think.  Charlie came down with diarrhea a couple days later, but I've never seen him eat anything but flowers from a vine we have in the backyard.  I've been cooking their food just in case the last couple of days.  I think until I have a sample tested from our yard, I'm going to keep cooking their food and working in the TO Wild & Natural and maybe the NV Raw Instinct.