In the many different species of mammals, yeasts contribute to the balance of the intestinal flora.
Researchers showed that, in mice, by removing a gene coding for a protein (Dectin 1), the yeast population of the mouse gut flora increased. Moreover, among the mice that developed colitis, symptoms were more severe than in controls.
Likewise, after antifungal treatment, symptoms were attenuated in mice with acute colitis.
While gut yeasts are harmless and beneficial under "normal" conditions, certain situations render them enteropathogenic.

This work opens up the pathway for a great variety of research in humans.

References
Published in the journal Science in June 2012