Frogs and Crocodiles are both Amphibians. Amphibians live in a very hostile environment. They are known to have tremendous immune systems.
It wouldn't surprise me that the frog is creating an environment that is protecting it from predators. These could include bacterial, fungal, helminth, or something larger like fish.
As I recall the Crocodile blood experiment used a bacteria grown in a petri dish. A single drop of blood Crocodile was placed in the center of the bacterial culture and observed. The results were remarkable.
You could spend many hours experimenting with this.