The negative role of bacteria.

Only a small fraction of the known bacteria are capable of causing disease. These bacteria are called pathogenic. To cause disease, bacteria must invade the cells of a living organism. Most bacteria will not invade another living organism, and many other bacteria are found to be harmless to our immune systems, while others, such as gut bacteria, are beneficial. In many developing countries, poor hygiene, limited access to clean water, and poor (or no) wastewater treatment result in a huge number of deaths from bacterial infections, such as those that cause dysentery.