What Are Bacteria in Human Life?

Bacteria are most widely distributed organisms. These are unicellular (organism that consists of one cell) micro-organisms. Leeuwenhoek discovered bacteria in 1677 for the first time. Later, Louis Pasture and Robert Loch worked on them. This was a milestone in the history of biology and medicine. Bacteria are among the smallest living thing on earth. Most bacteria measures from about 0.3 to 2.0 microns in diameter, and can only be seen through a microscope.

Classification of Bacteria
Scientists classify bacteria on the basis of shape and nutrition.

1. Classification on the basis of shape
There are different shapes of bacteria and on the basis of shape and form; bacteria can be divided into the following types.

Rounded Cocci (singular; Coccus)
Rod-like Bacilli (singular; Bacillus)
Spiral shaped Spirilla (singular; Spirillum)
Spiral shaped Spirochetes (singular; Spirochete)
Comma-shaped Vibrios (singular; Vibrio)

These types are given in the following table with pictures.

CLASSIFICATION OF BACTERIA ON THE BASIS OF SHAPE
Shape Name
Rounded Cocci
Rod-like Bacilli
Spiral Shaped Spirilla
Spirochete
Comma Shaped Vibrios

Bacteria are found singly and in colonies. Cocci bacteria may occur in groups of two or four, or in irregular groups and even in the form of long beads. Bacilli are found singly or may join end to form long treads. Spirilla, Spirochete and Vibrios however, occur singly.
2. Classification on the basis of nutrition
Some bacteria can manufacture their own food and are called autotrophic bacteria. Majority of bacteria are unable to make their food and obtain it from other living organisms and their dead bodies; they are know as heterotrophic bacteria.

2.1. Autotrophic Bacteria
The bacteria that can prepare their own food are known as autotrophic bacteria. Autotrophic bacteria can be further divided into two categories.

Photosynthetic Bacteria
Photosynthetic bacteria like all green plant manufacture their own food by photosynthesis. However, chemical structure of their chlorophyll is different from plant chlorophyll.

Chemosynthetic Bacteria
Chemosynthetic bacteria get energy by oxidizing compounds of sulphur, nitrogen and other inorganic substances and prepare their food. This process is called Chemosynthesis.

2.2. Heterotrophic Bacteria
The bacteria that cannot prepare their own food are known as heterotrophic bacteria. Heterotrophic bacteria can be further divided into two categories.

Parasitic Bacteria
The bacteria which live on other living organisms for their nutrition and survival are called parasitic bacteria. The parasitic bacteria also cause diseases in plants or animals are known as Pathogenic.

Saprotrophic Bacteria
Bacteria which obtain their food from dead organic matter are known as Saprotrophic bacteria.

Bacteria that need oxygen for respiration are called aerobic bacteria, while those, which do not require oxygen for respiration, are called anaerobic bacteria. Oxygen may rather be injurious for anaerobic bacterium.
Characteristics of Bacteria
Bacteria are so widespread that it is possible only to make the most general statements about their life history and ecology. They may be found:

on the tops of mountains
in the bottom of the deepest oceans
in the guts of animals
even in the frozen rocks and ice of Antarctica

One feature that has enabled them to spread so far, and last so long is their ability to go dormant for an extended period.

Bacteria need food, water and suitable temperature for their growth. Some bacteria, especially bacilli under unfavorable conditions form endospores inside their cell wall. Endospores is a tiny structure containing DNA, small portion cytoplasm and a tough protective coat and can resist unfavorable conditions by remaining dormant for many years. When conditions become favorable, the endospore develops into a new bacterium. Generally a bacterium reproduces asexually by simple division into two identical bacteria. Some bacteria also reproduce sexually.

Bacteria, like viruses are transferred from one living organism to another through different agencies like droplets, touch, contaminated water and food, insects and other animals.

Bacteria and Human Relationship
It is generally false impression that bacteria are harmful organisms. There are number of bacteria which are not only beneficial for mankind but are also essential for living system. The decision as to whether bacteria are friend or foe becomes more difficult when both the positive and negative aspects of the relationship between humans and bacteria are considered. Let's discuss three types of symbiotic relationships:

Commensalism
Commensalism is a relationship that is beneficial to the bacteria which live off of the host, but does not help or harm the host. Most of the bacteria that reside within the bodies of humans are commensalistic.

Mutualism
In a mutualistic relationship, both the bacteria and the host benefit. For example, there are several kinds of bacteria which live inside the mouth, nose, throat, and intestines of humans and animals. These bacteria receive a place to live and feed while keeping other harmful microbes from taking up residence.

Parasitism
A parasitic relationship is one in which the bacteria benefit while the host is harmed. Pathogenic parasites, which cause disease, do so by resisting the host's defenses and growing at the expense of the host. These bacteria produce poisonous substances called endotoxins and exotoxins which are responsible for the symptoms that occur with an illness.

When all of the facts are considered, bacteria are more helpful than harmful.
Beneficial Bacteria

Bacteria are of great ecological importance. These, along with fungi, help to decompose dead organisms and convert them into simpler substances replenishing the raw materials in the soil and atmosphere and can thus purify the environment.

Bacteria can add nitrogenous compounds in soil thus improving its fertility. These bacteria are called nitrogen-fixing-bacteria. Another kind of bacteria live in the soil called nitrifying bacteria which convert ammonia into nitrite and then to nitrate, enhancing the amount of nitrogen in the soil.

Bacteria are also used for industrial and commercial purposes, such as:

In manufacturing butter, cheese and yogurt.
In processing commercial fibers, leather, coffee, tobacco and vinegar.

Bacteria synthesize cellulose enzyme in the stomach of herbivore animals which helps in he digestion of food. Some bacteria also synthesize vitamin "B" and "K" in the large intestine of man and other mammals.

Recently the use of bacteria as bio-insecticides has become popular.

Bacteria help in the production of fuel in two major ways. Some bacteria decompose compost, garbage and sewage and help make methane. Methane is a valuable natural gas. It is used widely as a fuel. Also, over time, the earth's pressure has changed dead and decomposed animals and plants into coal, which is also a widespread fuel.

Bacteria are very important in medicine. Bacteria can actually help to fight themselves. Doctors and scientists have figured out how to use dead or weakened bacteria to prevent other bacterial diseases. This process is called vaccination. Vaccination has helped us all become a lot healthier then we were a hundred years ago. Bacteria also make, or help to make, drugs, hormones, or antibodies.

Harmful Bacteria
Bacterial decomposition on one hand is beneficial but on the other hand causes damage to food, wood, clothes and other things. Denitrifying bacteria in soil reduce the amount of nitrogen in soil thus damaging soil fertility. Many bacteria are harmful and are responsible for many diseases in plants, such as canker disease in citrus fruits; rot and fire blight in peach, pear and apple; and potato scab in potato.

In animal like cattle bacteria are responsible for T.B. and anthrax. Bacteria cause many diseases in man like T.B. whooping cough, diphtheria, typhoid, pneumonia, tetanus, plague, bacterial dysentery, cholera, leprosy, anthrax etc.

Whooping cough, diphtheria, T.B and pneumonia causing bacteria spread from one person to other person through sneezes and cough droplets released in air. Bacteria causing Typhoid and Cholera are transmitted from one organism to another through contaminated water and food. Plague and bacterial dysentery spread through vectors like flies and animals.

Food poisoning happens when someone eats food or drink that is contaminated with bacteria, or its toxins. Very occasionally, toxins from chemicals or pesticides can also cause food poisoning. It is hard to tell if food and drink are contaminated because the look, taste and smell may not be affected. Food poisoning can affect one person or a group of people, depending on whether they have all eaten the same contaminated food. Most food poisoning is caused by the toxins produced by bacteria, or by the amount of bacteria itself. Some bacteria can grow (multiply) from one to millions given the right conditions of moisture, food, warmth and time. The more bacteria present, the higher the chance of infection and illness. The most common types of bacteria to cause infection are Campylobacter, E.Coli and salmonella.

Septicemia is an infection of the blood often caused by bacteria. Sometimes known as blood poisoning, the bacteria in the blood release toxins than can have a serious impact on many organ systems. Signs include fever, shaking chills, and heavy sweating. Septicemia often occurs in patients with poor immune systems

At end I would like explain how we can decide an organism type is? Fist, we have to make pure colony. Then prepare slide put one drop of water on it. Use sterilized lobe to take a little bit of colony and then mix it with the drop of water on the slide to make a film. Leave it to be dry after that gram stain step which is has three stages first, put methyl violet for one minute then wash by water. Second, put iodine solution on the film for one minute then wash by water. Third, it is washed by 95% alcohol. Finally, put carol fascine stain for 30seconds then wash it by water. Leave it until dry then but one or two drops of oil on it. Put the slide under microscope to see their form and their colour.

Conclusion
In conclusion the essay presents definition of bacteria in general. That gives everybody some information about which huge things cannot see it. Moreover, where are they found them? In addition, why do bacteria important for people? In my opinion, the scientists still do not have all information about style life of bacteria. Consequently, every year they discovered a new type of organism. When we mention bacteria, most people think of germs and diseases. If asked to name an organism, most people don't mention bacteria - even though bacteria are the most numerous organisms on Earth! From what I have learned about bacteria, the earth would probably still be the barren wasteland it was 4.6 billion years ago if bacteria had never showed up. Bacteria started everything, and could very well end everything just as quickly. Bacteria do so much for us, where would we be without them?

REFERENCE LIST...
Internet links
http://encyclopedia.farlex.com/marker+bacteria
http://www.customessaymeister.com/customessays/Biology/1144.htm
http://www.ucmp.berkeley.edu/bacteria/bacterialh.html
http://biology.about.com/cs/bacteriology/a/aa032504a.htm
http://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=411
www.ucmp.berkely.edu/bacteria/bacteria.htmI
www.micro.msb.le.ac.uk/MBChB/3a.html
www.ulster.net/(mycoman/rbactnot.html

Bibliography
Aborn, Shana. "How Clean Is It?" Ladies Home Journal 114 (February 1997)
Brian, Dr. Tony and David Parker. "What Are Bacteria?" World Book's Young Scientist, 5, (1991)
Crockett, Lawrence J. "Bacteria" Academic American Encyclopedia 3, (1994)
Flannery, Maura C. "Back to Bacteria" The American Biology Teacher 59 (June 1997)
Neft, Naomi "Bacteria" Merit Student's Encyclopedia 2, (1990): 501 Rakosy, A.W. "Bacteria" Children's Britanica 2, (1994)
Raven, Peter H. and George B. Johnson. Understanding Biology. St. Louis: Times Mirror/Mosby College Publishing, 1988.
Schlessinger, David. "Bacteria" The World Book 2, (1990): 770.
Still, William B. "Bacteria" Encyclopedia of the Sciences 1, (1963): 75-77.
Ycas, Martynas "Bacteria" Collier's Encyclopedia 3, (1993): 444-448.