Examples of bacteria include Streptococcus, Staphylococcus, and Esherichia coli, commonly known as E. coli. All of these bacteria are pathogenic and cause infection in humans and animals. However, there are non-pathogenic bacteria as well.
Bacteria are living organisms that are comprised of one cell. Under a microscope they can have the appearance of rods, spheres or spirals. They are so small that over 1,000 bacteria could fit on a single pencil eraser. Approximately 1 percent of all bacteria found in the world are pathogenic. The rest are either helpful to humans or the world's ecosystem. Helpful bacteria can digest food for humans, synthesize vitamins and protect humans from disease.