Microorganisms are single-cell organisms that can only be seen under the microscope. They consist mainly of bacteria and archaeans but also include other lifeforms such as protists and some types of fungi. Their eating habits vary since they can be autotrophic (e.g. cyanobacteria), heterotrophic (e.g. paramecium), or in some cases even both (e.g. Euglena). They usually reproduce by RNA, and it happens extremely fast (est. every 20 minutes). There are exceptions to this rule, one of them being reproducing by spores. Some of these organisms are unable to move on their own and require outside force (water, air or other fluids), while some possess whiplike flagella that enable the cells to move toward nutrients, light and away from predators or other harmful chemicals. Since they are only made up of a single cell, that cell is responsible for all vital functions (nutrition, movement, breathing if needed, reproduction etc.).
Pathogens are a special subtype of microorganisms which only include disease-causing organisms. Bacteria, viruses, fungi and prions are the representative species for this category. You will notice that viruses fall into this category although they are not considered living organisms. These organisms are purely heterotrophic and very often parasitic. They invade the body of the host, usually entering by air, fluids or direct contact, and spread their characteristic disease. Their vital functions are not by any means different than the rest of the microorganisms, and the same goes for movement. The disease they spread depends on the species of the pathogen and is not limited to one since they can sometimes carry multiple (e.g. Lactobacillus).
Written by Tamara Bračko