When you don't know whether an animal was once a Carnivore, Omnivore, or Herbivore, all you have to look for is the teeth. Carnivores have long canines, as well as overall sharper teeth, while omnivores and herbivores contain flat molars.
I think the best medium is agar. It is a jelly-like substance that is obtained from algae, and is used to culture small organisms such as microorganisms and bacteria.
Hope this helps. :)
