This is my daughter's dog and she used A flea product (such as Frontline) on the dog (Lola) because she was scratching and my daughter found fleas. Then two weeks later my daughter put another dose on Lola because she wouldn't stop scratching and my daughter kept finding live fleas. I didn't know about this until last week when my daughter called me (we don't live in the same town) because she was worried about Lola's scratching and her poops looking slimy and bloody.
She brought her to the vet and I am not sure what tests were taken, I'll find out. They did prescribe metronidazole, although they haven't tested her stool yet, as my daughter didn't have a sample with her and the dog didn't go while there. They told her to start the metronidazole anyway and bring in the sample when she could.