Fungi truly are dimorphic in the field of veterinary medicine (although not all fungi are dimorphic, only the ones that exist in both a mold and yeast form). You can say this because fungi can both cause disease and treat disease, and in some cases the same exact one.

Say your dog is outside, running around the forest after a rainy night. She finds some mushrooms on a decomposing log in a shady area. Maybe she eats a few. Maybe she also sniffs a little puddle of urine from a wild animal (say a deer). Whoops! You call her back inside after seeing what went down. She comes back in.

A few days later she begins to show neurological signs and her eyeballs are yellow. You rush her to the emergency room, the veterinarian does some bloodwork and imaging, and they unfortunately diagnose her with acute liver failure secondary to mushroom toxicity.

The veterinarian tells you the mushrooms she ate most likely contained amanitin, which is the active, toxic component that causes acute hepatic necrosis and hepatocyte death. Ouch. After reminding the veterinarian about the puddle of urine your dog encountered, he decides to start her on penicillin, in addition to the other medications to support her liver.

Why?
Because Leptospirosis, the bacteria spread in the urine of wild animals, has been shown to also cause acute liver failure in dogs, and we could also be dealing with that here in addition to the mushroom toxicity!”
Got it.

With that, you think back to your Microbiology class in college and remember that penicillin, the broad-spectrum antibiotic, was originally obtained from the Penicillium molds P. chrysogenum and P. rubens. Interesting. Your dog probably doesn’t think so, but she’s just happy to be alive after a week in the hospital.