The term 'microbe' is used to refer to a variety of microscopic organisms, including viruses, BACTERIA, BACILLUS, and germs. A VIRUS is a small infectious agent that can replicate only inside the living cells of an organism. BACTERIA are single-celled microorganisms that can exist in diverse environments and can cause a range of illnesses. BACILLUS is a genus of Gram-positive, rod-shaped BACTERIA that can form endospores. Finally, a GERM is a microorganism, such as a VIRUS or bacterium, that can cause disease.