A pathogen is any organism or infectious agent that causes disease. They can be microscopic or macroscopic, and they can be found in a variety of environments.

Here are 3 types of pathogens:

1. Bacteria: These are single-celled organisms that can cause a wide range of diseases, from mild infections like strep throat to serious illnesses like pneumonia and tuberculosis. Examples: *Salmonella, E. coli, Staphylococcus aureus*

2. Viruses: These are even smaller than bacteria and are essentially genetic material (DNA or RNA) enclosed in a protein coat. They can only reproduce inside living cells. Examples: *Influenza virus, HIV, Coronavirus*

3. Fungi: These are eukaryotic organisms that can cause infections in humans, animals, and plants. They typically cause superficial infections of the skin, hair, or nails, but can also cause more serious systemic infections. Examples: *Candida albicans, Aspergillus fumigatus, Cryptococcus neoformans*