ECONOMIC IMPORTANCE OF BACTERIA

Most importance bacteria are harmless to humans, and many bacteria are essential or useful to the existence of plant and animal life. Only a small fractions of bacteria causes disease; most bacteria attack organic matter only after it is dead. Were it not for bacteria that decomposed animals and plants. These material would accumulate almost indefinitely. So many bacteria are useful for us, if no bacteria in this world, the world will full just in short time.

Bacteria also enrich the soil in various ways. The so-called nitrogen fixing bacteria take nitrogen gas fro the atmosphere and convert it to a form (nitrate) that green plants use for growth. Bacteria also create fertilizer by breaking down compost heaps made of soil and dead plat matter.

Bacteria are important industrially in the production of cheese, yogurt, buttermilk, vinegar, and sauerkraut; in the preparations of antibiotic such as streptomycin, which is extracted from soil bacteria; in the tanning of leather and hides and the curing of tobacco; and in the sewage disposal plants to render organic wastes harmless. Cattle, sheep, and goats live on the grass; yet without bacteria they would not be able to digest the tough fibers of plant cellulose.

Improperly processed foods are subject to spoilage by bacteria. Poisonous toxins are sometimes produced by such spoiling bacteria as staphylococci, Streptococci, and Salmonella. They cause severe illness human eating affected food. Clostridium botolinum, growing in canned or smoked foods that have been improperly processed, produces a toxin that causes Botulism, frequenly fatal disease.

BACTERIAL SENSITIVITY

The susceptibility of a given bacterial species to an antibiotic is usually determined either from laboratory tests or from the result of treating an establish ed infection.

In laboratory tests, bacteria isolated from an infected patient are inoculated into tubes containing a liquid culture medium enriched with graded concentration of an antibiotic agent. The lowest concentration of antibiotic that inhibit microbial growth is termed the minimal inhibitory concentration (MIC). When this is compared with concentrations attainable in the body, one can judge whether the bacteria are sensitive, partly sensitive, or resistant to the antibiotic. 

Alternatively, the surface of a semisolid growth medium can be inoculated with bacteria, and antibiotic-impregnated filter-paper disks placed on that surface. The antibiotic leaves clear zones around habited. The diameter of the inhibitory zones can be measured accurately and the results precisely interpreted.

Occasionally such tests do not correlate with clinical results, particularly when a person has a malignant disease, immune-system impairment, or severe injury, or is receiving drugs that reduce resistance to infection. Outcome may also be unpredictable because of failure to absorb the antibiotic, deterioration of the antibiotic during storage, or its inactivation by simultaneously administered drugs.

CLASSIFICATION OF ANTIBIOTIC

The most common classification is based on mechanism of action. Antibiotics that inhibit the growth of the bacterial cell wall include the commonly used penicillin and cephalothin groups, and such less-often-used antibiotics as vaconmycin and bacitracin. Antibiotic that act like detergent on the cell membrane-and therefore disrupt the passage of nutrients into the bacterial cell-include the antibacterial polymycin and colistin, and the antifungals mycostatin and amphotericin.

Antibiotics that interfere with protein synthesis in the bacterial cell include the tetracycline, the aminoglycosides (streptomycin, kanamycin, neomycin, gentamycin, amikacin) and the macrolide group comprising erythromycin, licomycin , and climdamycin. 

Antibacterials that disrupt bacterial gene replication include the antifungal griseofulvin to kill a fungi and the synthetic quinolone drugs.

Bactericidal and Bacteriostatic Effect

Another classification system is based on whether an antibiotic kills microorganism (bacterial effect) or merely inhibits growth (bacteriostatic effect). Penicillins, aminoglycoside, vanconmycin, bacitracin , the polymyxin, and colistin are bactericidal. Tetracyline, on the other hand, is bacteriostatic. When susceptible bacteria are exposed to tetracycline, growth will cease temporally and then resume. 

Chlorophenicol and the macrolides are also bacteriostatic. Lethal infectious diseases will respond only to bactericidal agents.

Spectrum of Activity

A further classification system rests on the effective target range (activity spectrum) of an antibiotic, as defined by two criteria;

1. The species of susceptible microorganism (for example, staphylococcus, streptococcus, and E coli)
2. Weather the species are gram-positive or gram-negative.

Bacteria retaining a blue stain despite treatment with iodine and acid alcohol are called gram-positive, and those losing it are gram negative. 

The penicillin are effective against most gram-positive bacteria, whereas aminoglycosides are chiefly effective against gram-negative bacteria. These two groups of antibiotics are therefore termed narrow-spectrum agents.

Tetracycline and chlorophenicol are effective agains a broad range of gram positive and gram negative bacteria, rickettsia, and other microorganism and are therefore called broad-spectrum antibiotics.

Bacteria Identification

Bacteria Identification is a special technique that is used by biologist and many other scientist, because many of bacteria is useful for human, beside the others can disadvantage for human. Beside can cause diseases, many bacteria type is need by human for food process or industrial uses. To make sure that the bacteria can useful for certain application, people must identify the bacteria that want to use.

An important, widely used technique for identifying bacteria is gram staining, perfected by the Danish bacteriologist Hans Christian Gram in 1884. In this process the bacteria are treated with a special dye, or stain, and other chemicals. The treated this microbe, bacteria fall into two groups, gram-positive bacteria, which appear deep violet in color. and gram-negative bacteria, which appear red in color. Physicians often use gram staining in choosing the proper Antibiotics for treating a bacterial infection. Gram-positive bacteria are more susceptible to penicilin, whereas gram-negative bacteria are usually more susceptible to other antibiotics such as streptomycin. The basis of this difference in staining properties is still a mystery, but evidence indicates that the difference lies in the composition of the bacterial cell wall.

Although bacterial and plant cells are enclosed by rigid walls, the walls differ in composition. Plant cell walls derive their strength largely from cellulose, whereas bacterial cell walls are stiffened primarily by murein (a compound made of amino acids and sugar). This is the basis for the selective activity of certain drugs such as penicilin. Nontoxic to plants and animals, penicilin is toxic to habitat growing of bacteria because it inhibits formation of murein and thus interferes with reproduction.

The Useful of Bacteria

There are two kind bacteria if see from the uses for human, benefit and disadvantage for human. Most of us think of bacteria as "germs" or microorganism, unseen threats to our health and welfare. But for each of the few disease-producing kinds which can live in the human body, there are hundreds of others upon which we depend for our very existence. Bacteria help us digest our food. Plant will die if no bacteria to convert leaf or other organic matter to humus.

Most kinds multiply by simply splitting in two: each bacterium dividing into two equal "daughter" bacteria every 20 or 30 minutes, under favorable conditions. Though microscopic in size, they can multiply so fast that, after a day and a half, the billions of offspring of a single one would load a long freight. Under unfavorable conditions, some kinds form thick-walled spores which can withstand prolonged drying, extreme cold, and even boiling; and may lie inactive for days or even years.

All animals depend upon plants, directly or indirectly. Plants depend upon the fertility of the soil, which in turn depends upon bacteria. Inconceivable numbers of them inhabit the soil -- roughly a billion per teaspoonful -- where some convert plant and animal remains into humus and plant food, and others make the minerals in the soil available as plant food. All decomposition and decay in the dead bodies of plants and animals are caused by bacteria and their close relatives: molds, fungi and yeasts. Our huge garbage dumps are decomposed by them. Our modern methods of sewage disposal employ speeded-up bacterial action to rapidly break down and oxidize household and industrial wastes.

Some of plant reside a kind of bacteria, Nitrogen in the form of nitrates is an essential plant food frequently lacking in soils. Nitrogen from the air is inert and difficult to change and combine with other substances, but certain bacteria have the rare ability to absorb it and change it into forms which other plants and animals can use.

Fermentation, as when wine and cider turn into vinegar, is caused by bacteria. Of hundreds of different kinds, a few of the common bacteria are those used to make rye bread, sauerkraut from cabbage, pickles from cucumbers, silage from corn, linen from flax, glycerin, citric acid, lactic acid, and dairy products.

Fresh warm milk is an ideal food for many kinds of bacteria, especially the common one which causes milk to sour and curdle. Cream so soured and ripened is easily churned into butter. Cottage cheese is made from sour milk. Most cheeses are made from curds produced by treating milk from cows, sheep or goats with "rennet", a digestive ferment. The ripening, and the different textures and flavors, are accomplished by various pure cultures of bacteria and molds which are added to the curd as "starters", depending also upon special conditions of air, moisture and temperature. Some extremely hard Italian cheeses contain little water and are correspondingly slow to ripen. "Soft" cheeses contain more water and ripen more rapidly. The blue-green mold of Roquefort is due to powdered bread mold sifted into the curd. The holes in Swiss cheese come from gas generated by bacteria.

Size and Habitat

Thirty trillion bacteria of average size weigh about 28 g (1 oz). Bacteria are measured in microns (0.001 micrometer, about 0.00004 in) and most types range from 0.1 to 4.0 microns in width and 0.2 to 50 microns in length. Bacteria are found every where. Approximately 2,000 species have been identified, many of them living in conditions that would destroy other organisms. They have been found in the almost airless reaches of the upper atmosphere, 10 km (6 mi) below the surface of the ocean, in frozen soil, and on rocks in hot springs. Some bacteria produce a resting stage, the endospore, which is the most resistant living thing known and can be killed only by boiling in steam under pressure for many hours.

Classification
Bacteria are neither plant nor animal. Both bacteria and plants have rigid cell walls, but unlike plants, most kinds of bacteria move about and use organic foods for energy and growth; only a few use photosynthesis.

On the basis of their shapes, bacteria may be grouped into three main type; the rod-shaped bacilli, which often have small whiplike structures known as Flagella that propel the organism; the spherical cocci (singular coccus), which may grow in chains (streptococci, or strep germs," as in strep throat) or which may clump together like a bunch of grapes Istrphylococci); and the comma or spiral shape spirilla and prirochetes (one of which is the cause of syphilis). Another kind of bacteria, the mycoplasmas, have no rigid cell walls and consequently are called pleuropneumonialike organisms, because they cause a contagious pneumonia in cows and human beings.