Who proved that microorganisms cause disease?

The person who proved that microorganisms cause disease was Louis Pasteur. He is known for his experiments that supported the germ theory of disease - the idea that microorganisms are the cause of diseases. Here are the steps he took:

1. Pasteur first hypothesized that diseases were caused by microscopic organisms not visible to the naked eye. This was a controversial idea at the time as the popular miasma theory suggested that diseases were caused by 'bad air'.

2. To prove his theory, Pasteur conducted a series of experiments. One of his most famous experiments involved broth. He prepared two sets of flasks - one with a straight neck and the other with a swan neck. He boiled the broth in both sets to kill any existing microorganisms.

3. After the broth cooled, microorganisms began to grow in the straight-neck flask where air (and dust carrying microorganisms) could easily enter. However, the swan-neck flask remained clear as the design prevented dust and microorganisms from reaching the broth.

4. Pasteur concluded from this experiment that the microorganisms that caused the broth to spoil came from the air, not spontaneously from the broth itself. This was a strong evidence supporting his germ theory of disease.

5. Pasteur's germ theory of disease laid the foundation for a whole new branch of science - microbiology. It also led to the development of vaccines and antibiotics, revolutionizing medicine.

So, it was Louis Pasteur who proved that microorganisms cause disease.