Types of Microbes – Which are Beneficial, and Which are Harmful?

Viruses, bacteria, fungi, and parasites sound pretty scary. These are the main categories of microbes, or tiny organisms. Some microbes have a bad reputation, including SARS-CoV-2, the virus that started the COVID-19 pandemic. But did you know that microbes are not all bad? Some of them are even helpful to our bodies!

Table of Contents

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What are the main types of microbes?

There are lots of different types of microbes. But they all have one thing in common. They cannot be seen with the naked eye, because they are extremely small. In other words, you need a microscope to see them. There are four main kinds of microbes.

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To start, viruses are an important microbe that we are very familiar with today. We learn about new types of the coronavirus and other viruses like influenza all the time. These viruses have caused serious sickness across the world. There are a few main features of a virus. Viruses have genetic material like DNA or RNA, and that genetic material is protected by protein. The protein is like armor for the DNA or RNA. Viruses also need a host to survive. This is because they do not have all the materials they need to replicate on their own. Apart from a host cell, a virus is not actually a living organism.

Virus Diagram

Bacteria, on the other hand, can be independent. They come with their own equipment, and they are unicellular organisms. This means that they have similar functions to single cells in your body. However, unlike cells in your body, bacteria do not have a nucleus that protects their DNA. Instead, their DNA floats throughout the cell. Even though bacteria can survive independently, they use host cells for nutrients and reproduction.

Bacteria Diagram

Fungi are even more complicated than bacteria. They are also more like our own human cells because they have a nucleus. Fungi tend to work in groups, so they can be multicellular, but they can also be unicellular. Similarly to bacteria, fungi are independent and do not need a host to survive. However, they can still infect a host like other microbes.

Fungi Diagram

Finally, you may have heard of parasites. These are microbes that feed off of a host and cause damage to that host. Like fungi, parasites can be unicellular or multicellular.

Parasite Diagram

How are microbes harmful?

Many microbes can cause disease. These are called pathogens. Disease-causing viruses include coronavirus, influenza, poliovirus, and many more. Different viruses can infect different types of cells in your body and lead to unique sickness. Viruses can cause trouble for your lungs, your stomach, and even your brain if they are allowed to replicate.

You may have also heard of some bacterial infections. For example, strep throat is caused by bacteria. When patients have strep throat, their doctors might give them an antibiotic. Antibiotics are special medications used to treat bacterial infections, but not other infections like viral infections. This is because antibiotics target the unique features of bacteria that viruses do not have.

"Mycobacterium tuberculosis Bacteria, the Cause of TB
"Mycobacterium tuberculosis Bacteria, the Cause of TB" by NIAID is licensed under CC BY 2.0

Before we had antibiotics, bacteria were a much bigger threat. For example, you may have learned about the Bubonic plague in history class, caused by bacteria. This terrible plague affected millions of people. Like viruses, bacteria can cause many different kinds of sickness from ear infections to breathing problems.

Next, there are not many fungi that are dangerous to humans. Fungal infections mostly affect people with weaker immune systems. One fungus that can affect humans is Aspergillus, which can cause stuffy nose, coughing, and breathing issues

"Aspergillus sp - Conidiophore" by gjshepherd_br is licensed under CC BY-NC-SA 2.0

Finally, most parasites are harmful to their hosts. They can cause damage in the body, leading to illness. Some are microscopic, but some are larger. An example of a microscopic parasite is giardia. One commonly known larger parasite that affects both humans and animals is tapeworms.

So when you hear about microbes in the news, it is no surprise that they’re mostly harmful ones. But what about all the microbes that don’t hurt us? What about the microbes that help us?

How are microbes beneficial?

Some microbes are actually helpful to our bodies and are not pathogens. Microbes live in all different areas of the body, including the mouth, skin, and stomach. As soon as a baby is born, it is covered by many microbes that can be completely harmless or even helpful. Every human has a unique collection of microbes that forms because of unique experiences.

What are some helpful jobs that microbes do for us? They can help us to break down food and get nutrients. Also, some harmless microbes can teach our immune systems what unfamiliar microbes look like in case more dangerous ones come along. One more way that these microbes can help us is by taking up space. If more harmless microbes cover our bodies, then there is less space for dangerous microbes to invade.

So while some microbes can cause trouble for us, most of them are harmless and even helpful to our bodies. We are not the only ones with collections of microbes, either! Animals, plants, soil, water, and even the atmosphere are all full of their own unique microbes.

Comparison Table

Comparison Table
Comparison Table

Fun facts about microbes

Want to learn about some cool microbes? Here are three that have special jobs throughout the world.

Yeast is a kind of fungus found in nature. But do you know what else yeast is found in? Food! If you bake bread or pastries, you might use yeast to fluff up your baked goods. That’s because this fungus likes to chew up the sugar in your baked goods and release carbon dioxide, which makes the bread rise.

Next, bacteria are everywhere. There are even some that can survive extreme temperatures like the hot springs in Yellowstone National Park! These bacteria help our environment by releasing oxygen

"Yellowstone hot spring
"Yellowstone hot spring" by Ian E. Abbott is licensed under CC BY-NC-SA 2.0

Lastly, did you know there are viruses in the ocean? They have very important jobs. Some viruses can kill dangerous plants in the water that cause disease for animals.


Microbe – a tiny organism

Virus – a microbe that needs a host to survive

Bacteria – a single cell microbe that can survive on its own, but uses hosts for nutrients and reproduction

Fungus – a microbe with multiple cells that can survive on its own

Parasite – a unicellular or multicellular species that uses and damages a host. They can be microscopic or larger.

Genetic material – DNA or RNA – a set of instructions for an organism

Unicellular – an organism that is only made of one cell

Multicellular – an organism that has lots of cells that work together

Nucleus – a pocket of a cell that protects genetic material like DNA

Pathogen – disease-causing microbe

Antibiotic – a special type of medication that treats bacterial infections

Immune System – the system that protects your body from disease

Flesch Kincaid Score: 60.1

Flesh-Kincaid Grade Level: 7.7


microbes final

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  • Tess Bub

    Tess Taggart Bub has a bachelor’s degree in biochemistry and a minor in data science from Houghton College. During her undergraduate studies, she conducted research in the areas of climate science, ecology, and muscle biology. She is currently a PhD candidate at the University of Tennessee Health Science Center studying host cellular response to viral infection. She is a strong believer that science can change the world, especially when it’s shared. In her free time, she loves communicating science, playing guitar and piano, and running. Writing for smore gives Tess the opportunity to help inspire a new generation of women in STEM.