bacteria

Microscopic single-celled organisms lacking a membrane-bound nucleus. Bacteria, like archaea, certain fungi, and viruses, are micro-organisms – organisms that are so small they can only be seen using a microscope. They are organisms that are more simple than the cells of animals, plants, and fungi in that they lack a nucleus. Bacteria are widespread, being present in soil, air, and water, and as parasites on and in other living things. Some parasitic bacteria cause disease by producing toxins, but others are harmless and can even benefit their hosts (see symbiosis). Bacteria usually reproduce by binary fission (dividing into two equal parts), and this may occur as often as every 20 minutes. Only a few thousand species of bacteria have been grown in laboratory cultures and characterized thoroughly, although genetic analysis of crude samples suggests that many millions of species may actually exist.Certain types of bacteria are vital in many food and industrial processes, while others play an essential role in the nitrogen cycle, which maintains soil fertility. They can be the first organism of a food chain, by acting as decomposers of dead plant and animal remains. This helps to recycle nutrients.

Bacteria can be grown on the surface of agar jelly in dishes in the laboratory and have been studied in detail. This has led to the development of antibiotics, chemicals that kill or inhibit micro-organisms such as bacteria. Sometimes the chemical is not harmful to humans and so can be used to treat disease. Some antibiotics work against a range of bacteria and in many situations, such as penicillins. Others are quite specific. For example, neomycin sulphate is especially active against bacteria that cause infections of the middle ear.

Due to the widespread and sometimes careless use of antibiotics, there are increasing numbers of bacterial strains that have become resistant to these. New antibiotics or alternative treatments need to be discovered so that antibiotic-resistant bacteria can be destroyed, but this is only occurring very slowly.