There are roughly four major types of microbes; fungi, bacteria, viruses, and parasites. Fungi are usually the largest in size. Bacteria are usually smaller than fungi and do not have a cell nucleus. Viruses are the smallest type of microbes that do not have a cell nucleus and a cell wall. Viruses can only reproduce inside a cell or other living organisms. Mushrooms and toadstools are also fungi.
One of the common microscopic parasites that can cause diseases are malaria parasites. Malaria parasites hide inside the human body where they multiply inside our blood cells. The malaria parasites spread when an infected mosquito takes a bite a person for a blood meal.
Though some worms are parasites, they are big and made up of many cells. They are not microbes.
Microbes are everywhere. It is estimated that there could be up to 10 thousand million bacterial cells in a gram of soil (10 thousand million = 10,000,000,000).[1] In our body, there could be up to 39 trillion bacterial cells (39 trillion = 39 million-million or 39,000,000,000,000).[2]
All germs can obtain the ability to resist the effects of medication that was once successfully used against them. This ability is called antimicrobial resistance.[3] For example, antibiotics are being overused in humans and animals, and these antibiotics are increasingly contaminating the environment. Exposure to antibiotics can induce a proportion of bacteria in our bodies, animals, and the environment to become antibiotic-resistant. These antibiotic-resistant bacteria can spread and cause fatal diseases.
Check out this video about microbes:
Microorganisms| The Dr. Binocs Show| Educational Videos For Kids
References
1 Ingham, E. R. (2019). Chapter 3: Bacteria. In Soil Biology. Retrieved from https://extension.illinois.edu/soil/SoilBiology/bacteria.htm.
2 Sender, R., Fuchs, S., & Milo, R. (2016). Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLOS Biology,14(8). doi:10.1371/journal.pbio.1002533
3 WHO. (2015). Global Action Plan on Antimicrobial Resistance. Geneva, Switzerland: WHO Document Production Services. ISBN: 978 92 4 150976 3