Bacteria are microscopic organisms believed to have been the only life form on Earth for 2.000 billion years. Its discovery is credited to Anton van Leeuwenhoek, a XNUMXth century Dutch scientist.
They are prokaryotes, that is, do not have a defined cell nucleus, and its size ranges between 0,5 and 5 micrometers, although thanks to microscopes it can be observed in detail, as well as the various forms it adopts: spheres, rods, corkscrews and propellers.
They once belonged to the animal kingdom, but were later placed in an independent kingdom, called the monera. Its study corresponds to bacteriology, a science that began to develop in the late nineteenth century as a result of medical research and fermentation processes, especially those of Louis Pasteur and Robert Koch.
The bacteria live in all living organisms, as well as for all the terrains of the planet, from the depths of the ocean to the highest mountain, because they adapt easily to any environmental condition. It is estimated that there are more bacteria on Earth than any other type of organism. Only in one gram of fertile soil, 2,5 billion copies can be reached.
People also have bacteria living inside us, especially on the skin and digestive tract. Some are beneficial and those that are not are usually nullified by the protective effect of the immune system. However it is not always so. Some pathogenic bacteria can cause disease infectious very dangerous to health, such as cholera or leprosy.