What is a pathogen and what are the 4 main types of pathogen?

A pathogen is a microorganism that causes a disease. The 4 main types of pathogen include: -viruses- eg. common cold, HIV- not alive because they do not complete the 7 life processes, made up of short lengths of DNA, infect hosts and replicate their DNA.-bacteria- e.g. gonorrhoea, salmonella- prokaryotic cells, bigger than viruses, not all are pathogens-fungi- e.g. athletes foot- eukaryotic, not all pathogenic e.g. yeast-protists- eg plasmodium protist (malaria)- these eukaryotic microorganisms have features that belong to animals, plants and fungi.