Skip main navigation

What are microbes?

A microbe is a micro-organism with microscopic or sub-microscopic size, meaning it cannot be seen by the naked eye.
Person in laboratory looking at a sample through a microscope
© BSAC

Here, we will define what microbes are and look at the different types of microbes. A microbe is a micro-organism with microscopic or sub-microscopic size, meaning it cannot be seen by the naked eye.

What are the different types of microbe?

Viruses are dependent on cellular synthesis machinery to replicate. This can often, but not always, result in cell death. Examples of viruses include measles, influenza, HIV, and Zika.

Bacteria are prokaryotes, meaning they lack a nucleus or other organelles. Most, but not all, are free-living. Examples of bacteria include tuberculosis, skin and wound infections pneumonia, and diarrheal diseases.

Fungi are eukaryotes, meaning they have nuclei and organelles. Fungi can exist as yeasts or moulds: yeast are single-celled organisms (e.g. Saccharomyces cerevisiae), while moulds form tubular extensions known as hyphae (fuzzy structures seen on old bread). Most fungi are larger than bacteria, and they have a rigid external cell wall and generally grow more slowly than bacteria. Examples of fungi include vaginal and oral candidiasis, fungal meningitis, aspergillosis, athlete’s foot, and toenail fungus.

Protozoa are single-celled eukaryotes and can be differentiated from algae because they are unable to carry out photosynthesis. Examples of protozoa include malaria, leishmaniasis, and giardiasis.

Prions are misfolded proteins with the ability to transmit their misfolded shape onto normal variants of the same protein.

Size comparison of microbes

Virus Bacteria Fungi/Protozoa
0.03-0.3 μm 0.1 – 10μm 4 – 10μm
Electron microscope Light microscope Visible to naked eye

 

© BSAC
This article is from the free online

Introduction to Practical Microbiology

Created by
FutureLearn - Learning For Life

Our purpose is to transform access to education.

We offer a diverse selection of courses from leading universities and cultural institutions from around the world. These are delivered one step at a time, and are accessible on mobile, tablet and desktop, so you can fit learning around your life.

We believe learning should be an enjoyable, social experience, so our courses offer the opportunity to discuss what you’re learning with others as you go, helping you make fresh discoveries and form new ideas.
You can unlock new opportunities with unlimited access to hundreds of online short courses for a year by subscribing to our Unlimited package. Build your knowledge with top universities and organisations.

Learn more about how FutureLearn is transforming access to education