Bacteria are microbes comprising a vast realm of prokaryotic micro organisms. Usually, they are only a few micrometers long and appear in various different shapes varying from spheres, to spirals and rods. It is said that bacteria were the first life forms on Earth and presently exist in nearly all types of habitats. Bacteria can be found inhabiting the soil, water, radioactive waste substances, acidic hot springs and also in the deep regions of the Earth's crust. In addition, bacteria are also found living in parasitic as well as symbiotic relationship with animals and plants. According to reports, bacteria have also succeeded in flourishing in manned spacecraft.

As discussed above, bacteria are minute organisms, typically comprising a solitary cell and without any chlorophyll (the green phytochemical that enables plant to make their own food). They along with viruses are the smallest living organisms on Earth. In fact, several bacteria are so minute that laying a million of them end-to-end would only measure about 5 cm (two inches).

Bacteria are omnipresent and they can be found in the soil, water, air, on your skin as well as within your body. Bacteria, like many other microbes, have a tendency to multiply very fast, especially when the conditions are favourable. They form colonies, each comprising several million or even billion of microbes, and usually occupying a space as small as a water droplet.

Anton van Leeuwenhoek (1632 - 1723), a Dutch merchant who was also an amateur scientist, is credited to be the first person who observed bacteria as well as other microbes. He designed a single-lens microscope to observe these micro organisms. Leeuwenhoek used the term "animalcules" to describe bacteria as well other micro organisms in the series of letters he wrote to the Royal Society of London during the period between 1674 and 1723.

Currently, bacteria are placed in the class known as Procaryotae. The term procaryotae denotes that bacteria are composed of prokaryotic cells - cells that do not contain a nucleus. For the uninitiated, a nucleus is basically a structure that regulates the functioning of a cell and encloses genes, which carry the deoxyribonucleic acid (DNA). The DNA is the substance that determines the attributes that are passed on from the parent to the offspring. On the other hand, the genetic substance of bacteria is enclosed in a solitary, spherical DNA chain.

Harmless, useful, and harmful bacteria

Often, bacteria are classified depending on their effect on human life. While a number of bacteria are beneficial for humans and are used to provide nutrients that enhance human's health, there are others that are responsible for various diseases. There is a third type of bacteria and these do not have any overall effect on the health and life of humans.

Beneficial bacteria: Bacteria present in the gut of several animals promote digestion of ingested foods. For instance, animals like cows, sheep, deer and other ruminants all have a large organ called the rumen, which is inhabited by bacteria. These bacteria facilitate the breaking down or metabolism of cellulose fibers as well as other coarse plant materials. In the case of the humans, the bacteria type called Escherichia coli (E. coli) can be found all over the digestive system. E. coli helps to break down several types of ingested foods. In addition, bacteria also stimulate the production of a number of vitamins in the body, including vitamin K and specific B vitamins.

Moreover, specific types of bacteria are also necessary for the crumble as well as decomposition of waste substances. These types of bacteria are called decomposers, which invade the dead materials and disintegrate them into simpler materials, which can be used by plants as nutrients.

Last, but not the least important, bacteria also play a vital role in producing several foods consumed by humans. For instance, bacteria helps to make milk sour and, hence, are used for producing buttermilk, curd, cheese and yogurt. In fact, the action of bacteria on cabbage and ethyl alcohol results in the production of sauerkraut and vinegar, respectively.

Harmful bacteria: Although it may seem interesting, most people are familiar with bacteria because they are responsible for various diseases in plants as well as animals. Some diseases occur in plants and animals when bacteria infect them directly. For instance, vegetables and fruits become discoloured while growing following bacterial infections.

Aside from directly attacking plants and animals, bacteria also afflict them by discharging chemicals that are noxious for plants and animals. Such poisonous chemicals are known as toxins. Clostridium tetani is a very common bacterium that produces and secretes toxins, which are accountable for the condition known as tetanus. Commonly also called lockjaw, tetanus paralyzes the muscles of affected people. Another bacterium called Clostridium botulinum, which is related to Clostridium tetani, also produces a toxin that leads to one of the most severe types of food poisoning known as botulism.

You will be alarmed to know that a number of dangerous types of bacteria survive on our skin. However, they are unable to cause us any harm till they get into the blood stream via any crack or break in our skin. Staphylococcus is one such bacteria type and it causes a toxic shock syndrome, which is potentially fatal. While E. coli is beneficial for us when it remains inside the digestive system, it may cause diarrhea, cramping and even turn out to be fatal when it enters our blood stream from ingested foods.

Nearly all types of food preservations, including drying and freezing, are meant to eliminate bacteria or render them inactive. If this is not done, bacteria will either make the food rancour or result in various types of disease from the infected foods. Pasteurization is a very common and widely used technique to destroy bacteria present in food. The process of pasteurization involves heating the food product to a specific temperature for a particular period of time and subsequently cooling it. The temperature as well as the time period is chosen in such a way so that one can be certain that any or all bacteria present in the food product are destroyed completely. In fact, pasteurization of milk has helped us to supply this vital and popular food product to distant places without it getting decomposed.