1. Bacteria: These are single-celled organisms that can cause a wide range of illnesses, from food poisoning to pneumonia.

2. Viruses: Even smaller than bacteria, viruses are not considered living organisms and need a host cell to reproduce. They cause illnesses like the flu, common cold, and COVID-19.

3. Fungi: Fungi are multicellular organisms that include yeasts, molds, and mushrooms. Some fungi can cause infections like athlete's foot and ringworm.

4. Protozoa: These are single-celled organisms that can cause illnesses like malaria and giardiasis.

5. Parasites: These are organisms that live on or in a host and benefit from the host, often harming it in the process. Examples include tapeworms, lice, and fleas.

Remember, these are just the major types of germs. There are many different species within each category, each with its own characteristics and ways of causing illness.