Bacteria are single-celled microorganisms that contain all the basic building blocks of a cell, such as DNA, RNA, cell walls, and cell organelles. The word bacterium is the singular form for the plural form bacteria. Bacteria reproduce by dividing their DNA and RNA into two parts and then building up cell walls to divide the one cell into two cells.
Bacteria are all around us. They are everywhere: on your skin, in your nose, in your intestines, and on every object that you touch or eat. But don’t worry. Most bacteria in the world are either helpful from the perspective of humans (such as bacteria that break down waste products) or at least not harmful. Bacteria that are harmful to humans are relatively rare. About 40 percent of the vaccines available in the United States are targeted against harmful bacteria.