Frogs have helpful bacteria living on their skin that can fight dangerous water molds called Saprolegnia. Scientists discovered that different types of bacteria, especially Bacillus species, can prevent these molds from growing. The study found that frogs from polluted or salty water actually had bacteria that were better at fighting the mold, likely because harsh conditions helped tougher bacteria survive. These protective bacteria might explain why adult frogs can resist these infections better than tadpoles or eggs.