Bacteria are a form of microorganism that can be visualized only with the help of a microscope. Usually, bacteria live on the skin, genitalia as well as the intestines. All bacteria do not cause harm, some are good for us to maintain our health. Only certain types, classified as pathogenic bacteria, cause infections and diseases.

Bacteria are single-celled creatures that can reproduce on their own. They have a rigid wall, and a thin membrane surrounds the cell fluid. It has existed for many years and can live in any environment like the human body, radioactive waste and also in extreme climatic condition. We find in history how people have been affected by the Black Death and the bubonic plague caused by the bacteria known as Yersinia pestis.