Bacteria are unicellular living organisms. They are microscopic and hence cannot be seen with naked eyes. They are spread all over the world and thrive in almost any environment. Bacteria are mostly harmful; however, there are certain useful bacteria as well. Some of the common harmful bacteria are disease-causing bacteria that cause cholera, pneumonia, diphtheria and typhoid. Some useful bacteria are cultivated for human use. For example, the ones which cause the decay of dead plants and animals, those which carry out fermentation in cheese, cream, sour milk, etc. Bacteria can be classified according to their shapes; for example, coccus (spherical), bacillus (rod-like), and spirillum (curved).
What are Bacteria?
