1.1 What is a microbe? The word microbe (microorganism)is used to describe an organism that is so small that can not be seen without the use of a microscope. Viruses,bacteria,fungi,protozoa and some algae are all included in this category.The word microbe (microorganism) is used to describe an organism that is so small that can not be seen without the use of a microscope. Viruses, bacteria, fungi, protozoa and some algae are all included in this category. 1.1 What is a microbe?