Importance of Bacteria

In research technology

Bacteria are used in biotechnology. Escherichia coli are used in gene cloning. Agrobacterium tumefaciens is used in producing transgenic plants such as Golden Rice which prevents blindness that occurs in those whose diet is deficient in vitamin A. Golden Rice contains beta-carotene, a precursor of vitamin A.Bacteria are used as agent in bioremediation. They are used to 8m remove pollutants from soil, air and water. Anaerobic bacteria decompose the organic matter in sewage and convert it to such material that can be used as fertilizer. Bioremediation applications include cleaning up of oil spills and precipitation of radioactive material in groundwater. Bacteria play important role in plastic industry. Billions of pounds of plastics are produced from petroleum and used in making toys, containers, bottles and other items. These products degrade slowly creating environmental problems. Bacteria are now used to make natural plastics which are biodegradable.

Bacteria are modified by genetic engineering to produce vitamins,antibiotics, hormones and other products. Humulin, human insulin is produced by using recombinant DNA technology. It also helps in producing disease resistant crop plants. Ethanol is used as a substitute of fossil fuel.Bacteria help to produce ethanol from various forms of biomass such as agricultural wastes, willows and corn.

ii. As nutrient recyclers

Saprophytic bacteria are decomposers. They break down organic compounds like proteins and carbohydrates into simpler compound like co, which is released in the atmosphere for recycling. It is fixed by green

plants in photosynthesis. Other nutrients released in the process enter the soil and become available to plants. Bacteria can decompose the dead remains of plants and animals. Because of their cleaning action they are called the scavengers of planet earth. In sewage treatment, the bacteria

bring about the break down of organic compounds and convert them into

harmless ions such as nitrates and sulphates.

iii. Role in Ecology

Bacteria play important role in ecological interactions. They are involved in symbiotic nitrogen fixation in the roots of leguminous plants.Herbivorous mammals cannot break down cellulose. Bacteria live in their

guts and help in the digestion of cellulose by breaking it down. The relationship is called commensalisms. Soil bacteria decompose the organic matter and make the soil fertile. Bacteria also play important role in nitrogen, phosphorus, sulphur and carbon cycles.

iv. Other uses of bacteria

Bacteria are used in the preparation of diary products such as butter,cheese and yoghurt. They are involved in the preparation of antibiotics,vinegar, amino acids and proteins. Bacteria are employed in retting of

fibers and making of silage.

v. Spoilage of food

Bacteria spoil the food items. Foods with high protein contents are decomposed by bacteria. Eggs, fish and cooked food and milk are all spoiled by bacterial action.

Bacterial Diseases in Humans

A relatively small number of bacteria are the cause of many serious diseases of human beings. These diseases are transmitted in four main ways: Airborne bacterial diseases include diphtheria, tuberculosis, bacterial pneumonia and whooping cough. Water borne bacterial diseases are typhoid fever, gastroenteritis, dysentery and cholera. The food borne diseases include botulism and many types of food poisoning. In some

diseases like erysipelas, the infection occurs through wounds or cracks in the skin.

Bacteria cause illness by producing poisonous substances which are called exotoxins and endotoxins. Exotoxins are proteins secreted by the cytoplasm of living cells into medium. Endotoxins are lipopolysaccharide complexes present in the cell wall as constituent in Gram-negative bacteria. In contrast to exotoxins, the endotoxins are released only when bacteria die and their cells break down.

Some of the diseases caused by the bacteria are discussed below.

1. Cholera

Cholera is caused by Vibrio cholera, a curved Gram-negative bacterium. It enters the intestinal tract from contaminated water and food. Bacteria secrete a toxin that stimulates the loss of fluid. Massive diarrhea is associated with cholera. In severe cases a victim may lose up to one liter of colourless and watery fluid per hour for several hours, the eyes of the patient become gray and sink into their orbits. The skin is wrinkled,

becomes dry and cold and muscular cramps occur in arms and legs. The blood is thickened and urine production ceases and patient goes into coma.In untreated cases mortality may reach 70 percent. Antibiotic such as tetracycline may be used to kill bacteria. In severely dehydrated cases oral

dehydrated solution (RS) is given to restore the normal balance of water and salts.

The most important preventive measures include sanitation,personal hygiene and care in food preparation. Immunization against the disease gives protection for about six months.

2. Typhoid fever

Typhoid fever is a disease which has ravaged humans for Salmonella typhi. This bacterium causes disease only in humans and is generations. It is caused by a rod-shaped Gram-negative bacterium called

transmitted by five Fs, flies, food, fingers, feces and fomites( an object or substance that serves to transfer infectious organisms from one individual to another). Widal test is used for diagnosis. The symptoms of the disease mounting fever and lethargy. The abdomen becomes covered with red are ulcers and blood in stools but little diarrhea. The patient experiences spots, an indication that blood is hemorrhaging in the skin. At a later stage,gall bladder is also infected. The treatment of typhoid fever is generally

successful with antibiotic chloramphenicol, however it has recently been replaced by other antibiotics. Vaccines are available for immunization.

3. Tuberculosis (TB)

Tuberculosis has remained a great killer disease for thousands of years. Generally the people living in Slums and suffering from malnutrition contract tuberculosis. Poor quality of life and overcrowding increase the

chances of occurrence of disease in a locality. Tuberculosis is caused by

Mycobacterium tuberculosis which is an acid-resistant bacillus bacterium.The patient experience chronic cough, chest pain and high fever and expel sputum which is rush-eotoured mucous indicating the entrance of blood in to lungs. A hard nodule called tubercle is formed in the lung. The tubercle

expands and the lungs slowly deteriorate. The basic principle of TB treatment and control is to make sure that the patient completes a full course of medication so that all the bacteria causing infection are killed and drug- resistant strains are not allowed to develop. TB patient are largely treated

with isoniazid (isonicotinylhydrazine (INH) ) and rifampin and to a lesser extent by ethambutal and streptomycin. The drug administration is supplemented with good meal and living condition. Immunization to

tuberculosis is rendered by injecting the vaccine called Bacille Calmette Guerin (BCG).

4. Pneumonia

The term pneumonia refers to a microbial disease of bronchial tubes and lungs. Many organism including viruses and bacterial may cause pneumonia. But over 80 percent of bacterial cases are due to Streptococcus

pneumoniae which is capsulated gram-positive bacterium. The disease is commonly called pneumococcal pneumonia. The diseased person is usually acquired by droplets or contact with a diseased person. The patient with pneumonia experience high fever, sharp chest pains, difficulty in

breathing and rust- coloured sputum. The blood seeps into the alveolar sacs of the lung and the lung tissue gradually deteriorates. The drug given to pneumonia patients is penicillin with tetracycline and chloramphenicol used for people who are allergic to penicillin. About 80 strains of

Sreptococus pneumoniae cause pneumonia, but the vaccine for immunization to only 23. strains is now available.

Some important bacterial diseases of plants.

1. Bacterial leaf spots

Cucurbits beans, corn and many other plants are infected by Pseudomonad spp. causing leaf diseases. The infected plant parts are leaves,stems, fruits and seeds. Symptoms of

disease are different in different plants some

have small spots of different colours on their

leaves. In peppers and cucurbits, as the

disease progresses, large irregular holes

appear in leaves. The conditions favorable

for the development of leaf spot disease are:

warm temperature, frequent rains, high

relative humidity, use of diseased seeds, over-crowding of plants and poor soil drainage. Preventive measures include erop rotation hot water seed treatment uses of disease free seeds and removal of infected plants.

2. Bacterial will

The causal organism of bacterial wilt disease is Ralstonia solanacearum

and the host plants are potato, tobacco,

bringal, banana, cotton, sweet potato

and others. The disease symptoms differ

from plant to plant. In tomato and

bringal, initial symptoms of disease are

the wilting of terminal leaves and after

2-3 days entire plants wilt. In potato the plant wilt quickly without yellowing. The conditions which are ideal for the development of disease

are: leaving the infected crop residues in the field, warm temperature, high moisture contents of soil, high soil pH and

and infertile soil. Preventive measures of disease are: destroying the poor

infected plants immediately, crop rotations, control of nematodes and use of

disinfected farm tools.

3. Bacterial soft rot

Soft rot disease of potato, sweet potato, onion ,carrot, tomato, beans, corn,cotton and crucifers is caused by Erwinia carotovora. The infected parts and the symptoms of disease differ in different plants. In cruciters, generally the petiole is infected which becomes soft, spongy and dark in colour. In carrot, the taproot is infected; it becomes soft and watery and sometime it is lost completely. The infected plant of corn becomes dark brown. Water-soaked

soft stalk suddenly collapses and become twisted.The initial signs of disease are premature withering and drying up of the tips of uppermost leaves, then

the lower leaves, soon followed by the appearance of a slimy soft rot at the bases of leaves. The infection in potato converts the tuber into cream to tan coloured soft tissues. Preventive measures are preparation of properly drained soil, control of nematodes, removal of infected plants immediately, crop rotation etc.

4. Bacterial galls

Galls caused by bacteria are a very small

but important group of bacterial plant pathogens.Most common is crown gall caused by Agrobacterium tumefaciens, which is a soil-inhabiting bacterium. The bacterium causes abnormal growths or galls on roots, twigs and branches of plants of family rosaceae. The bacterium stimulates the rapid growth of plant cells that results in the galls. Galls are most commonly found near ground level on roots and lower branches of the plants. As the galls enlarge,

they become woody and hard. The plant becomes weak and stunted. Symptoms of disease may not develop immediately after infection. Galls grow most rapidly during warm months of the years. The disease can spread through contaminated soil and tools.

5. Bacterial blights

Bacterial blights on different plants are known by different names and are caused by different species of bacteria. The plants infected by blight disease include wheat, barley, oat and beans. Common bacterial blight on beans is caused by Xanthomonas

campestris pw. Phaseoli. Symptoms of disease first appear on leaves as

small water soaked light green spots.

The spots enlarge and the tissue in the centre dies and turns brown. These irregularly shaped spots are bordered by lemon yellow ring. The spots grow, leaf dies and is shed and plant is defoliated.

Common bacterial blight is favoured by

conditions of high moisture and humidity.

Control measures include use of tested seeds

practice of crop rotation, avoidance of overhead irrigation and the elimination of crop residue.

Bacterial flora of humans

The assemblage of microorganisms that constantly and consistently inhabit the human body is called human flora. They include bacteria, fungi and other organisms. Some of these organisms are known to perform tasks that are useful for the human body, while most of them produce no known

beneficial or harmful effects. The microorganisms which are expected to

be present and under normal circumstances do not cause disease are considered as member of the normal flora.

Benefits of normal Bacterial flora

1. Normal flora synthesizes and excretes vitamins in excess of their

own needs. These vitamins are absorbed as nutrients by the human body.

2. It prevents colonization of pathogens. by competing for attachment sites or for essential nutrients. In this way the normal flora of the care protein protein) human organs inhibits the growth of pathogenic bacteria through competitive exclusion. This is thought to be the most important beneficial effect of normal bacterial flora.

3. Normal flora of bacteria may antagonize other bacteria through en locality

production of substances which inhibit or kill non-indigenous bacteria. The intestinal bacteria produce many substances which inhibit or kill other bacteria.

4. Normal flora stimulates the production of natural antibodies, inducting immunological response. Such antibodies are lacking in germ-free individuals.

Control of Harmful bacteria

Although the disease-producing nature of bacteria become known

100 years after their discovery largely because of the research of Louis Pasteur and Robert Koch, however the early civilization used some crude techniques such as salting, smoking, picking, drying and exposure of food and clothing to sunlight to control microbial growth. Today microbial growth is controlled by physical and chemical methods.

A. Physical method

i. Heat treatment

Heat kills the microbes by denaturing their enzymes and otherproteins. Moist heat is much more effective than dry heat. Boiling is more effective. Heating to 100°C or more kills vegetative forms of bacterial pathogens within 10 minutes. Sterilization of surgical instrument requires temperatures above

that of boiling water. Autoclave chambers used for sterilization are filled with hot steam under pressure. Pasteurization is a process to prevent the spoilage of beverages

such as juices, milk, wine etc. the process has recently been improved and is called high temperature short time pasteurization (HTST). Milk is exposed to 72°C for 15 seconds. However a much more effective method of pasteurization of milk is through ultra high temperature (UHT) in which

milk is treated at 140°C for 3 seconds and then cooled suddenly in a vacuum chamber. Milk treated by UHT can be stored at room temperature for several months.

Dry heating by direct flaming to kill the microbes is used to sterilize inoculating loops and needles. Incineration is dry heat treatment of sterilization of disposable items such as paper cups, dressing etc. the

contaminated items are placed in an oven at 170°C for 2 hours to kill microbes.

Filtration

Filtration is the removal of microbes by passage of a liquid or gas through a screen like material with pores. It is used to sterilize heat sensitive material like vaccines, enzymes, antibiotics etc.

i. Low temperature treatment

Refrigeration at temperature 0°C to 7°C reduces activities of microbes, they cannot reproduce or produce toxins. It is called bacteriostatic effect.

Desiccation

Water is extracted from the contaminated material. In the absence of water, bacteria cannot grow or reproduce.

Osmotic pressure treatment.

The high concentration of salt or sugar in food increase its osmotic pressure and creates a hypertonic environment which helps in controlling the growth of microbes.

Radiation

Three types of radiation ie ionizing radiation, ultraviolet light and

microwave radiation are used to kill microbes.

2. Chemical methods

Different groups of chemical are used for disinfecting various products

1. Phenolics are effectively used against Gram-positive bacteria in nurseries but their excessive use in infants is harmful.

2. Among halogens, chlorine is used to disinfect drinking water and pools. Tincture iodine is one of many antiseptics used.

3.Alcohols kill bacteria and also evaporate leaving no residue. They wipe microbes off skin before injection or blood drawing.

4.Heavy metal include copper, selenium, mercury and zinc are used as disinfectants against skin wounds, in pools, fish tanks, dandruff shampoos and mouthwashes.

5.Formaldehyde (formalin) is widely used to preserve biological specimens. It inactivates bacteria in vaccines. Glutaraldehyde is less

irritating but more effective than formalin. It is used to disinfect hospital instruments.

6.Ethylene oxide kills all microbes and endospores but requires 4-18

hospital instrument hours exposure.

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