VIRAL DISEASES AND IMMUNIZATION

The discovery of viruses and their role in disease was made possible when Charles Chamberland(1851-1908),one of Pasteur's associates constructed a porcelain bacteria filter in 1884.

The first virus to be recognised as filterable was Tobacco Mosaic Virus,discovered by Russian,named Ivanovski(1882) and by Bejernick (1899) in Holland.On the other hand,filterable animal viruses were discovered for foot  and mouth disease of cattle by Loffer and Frosch(1898),and for a human disease,yellow fever by the US  army commission.Twort in England and D'Herelle in France in 1916-1917 discovered viruses that infect bacteria i.e. bacteriophages.The first crystallisation of virus was made by Stanley(1935).

After this discovery,it was a matter of great surprise too the scientist that how animals resisted disease.Pasteur observed that old cultures of the bacterium attenuated i.e. lost their disease causing ability,they remain healthy but developed the ability to resist disease.He called the attenuated culture as Vaccine in respect of Edward Jenner because,several years back Jenner had used vaccination with material from cowpox lesion to protect people against smallpox.Emil Von Boehring(1854-1917) and Shibasaburo Kitasato(1852-1931)used inactivated toxin into rabbit,inducing them for antitoxin production.This is how a tetanus antitoxin was prepared and now used in treatment. 

GERM THEORY OF DISEASES

The 'germ theory of disease' has presented a great stimulus in Microbiology and Medicine. Louis Pasteur and Robert Koch(1843-1910) were the national heroes.Preventive measures also supported the germ theory.Edward Jenner(1796) introduced vaccination against small pox,using material from lesions of a similar disease of cattle(cowpox).In 1860s,Joseph Lister introduced antiseptic surgery,on the basis of Pasteur's evidence for the ubiquity of airborne microbes.

Recognition of agents of infection first to be  recognised were fungi:Agostinod Bassi(1836) demonstrated that a  fungus was the cause of disease(of silk worm),the etiologic role of bacteria was established by Koch(1876) for Anthrax.The pure culture preparation is the key to the identification.Koch preferred the technique of identification including the use of solid media and the use of stain.After identifying the tubercle bacillus Koch formalized the criteria,introduced by Henle in 1840 but known as Koch's postulates,for distinguishing a pathogenic from an adventitious microbe:

                                  1. The organism is regularly found in the lesion of the disease.

                                  2. It  can be isolated in pure culture.

                                  3. Inoculation of this culture produces a similar disease in experiments on animals.

These criteria have proceeded invaluable in identifying pathogens,but they cannot be met:some organism such as viruses cannot grow on artificial media and some are pathogenic only for man.

Golden era of microbiology was established between 1860 and 1910 because of development of powerful methodology.

Moreover,various members of the German school isolated,the Cholera Vibrio,Typhoid Bacillus,Diphtheria,Bacillus,Pneumococcus,Staphylococcus,Streptococcus,Meningococcus,Gonococcus and Tetanus bacillus. 

GOLDEN ERA OF MICROBIOLOGY

Golden era of microbiology started with the work of Louis Pasteur(France)and Robert Koch(Germany). Louis Pasteur(1822-1895) investigated number nuber of aspects such as he showed that boiled medium could remain clear in a swan-neck flask,open to the air through a sinuous horizontal tube in which dust particles would settle as air reentered the cooling vessel.Pasteur also demostrated that in the relatively dust free atmosphere of a quite cellar,or of a mountain top, sealed flasks could be opened and then released so as to avoid contamination.

Pasteur delivered a lecture in 1864 at Sorbonne and made sensation by discovering life  is a germ and germ is a life. F.Cohn(1876)studied the biology of bacilli. John Tyndal(1820-1893)shoowed thhe hay had committed his lab with an incredible kind of living organism. Ferdinand John(1877)demonstrated the resistant forms as small, refractile endospores, a special stage in the life cycle of hay bacillus(Bacillus subtilis).Since spores are readily sterilized in the presence of moisture(at 120degree celcius),the autoclave,which uses steam under pressure,became hallmark of the bacteriology. 

Pasteur(1857) became interested in fermentation products and observed different kind of microbes associated with different kind of fermentation:spheres of variable size(yeast cells)in the alcoholic fermentation,and smaller rods(lactobacilli)in the lactic acid fermentation.During this experiment,Pasteur established the study of microbial metabolism and in particular he showed that life is possible without air.Pasteur explained that in grape juice the high sugar concentration and the low protien content(i.e.low buffering power)lead to a low pH,which allows the outgrowth of acid-resistant yeasts and thus yields an alcoholic fermentation.In milk,in contrast,the much higher protien and lower sugar content favour the outgrowth of fast growing but more acid-sensitive bacteria,which cause a lactic acid fermentation.This finding led Pasteur to state that specific microbes might also be causes of specific disease in man.

Pasteur developed the procedure of gentle heating(i.e.pasteurization)to prevent the spoilage of beer and wine by undesired microbes.This process was later used to prevent milk borne diseases of man.Of the great economic importance was the extention of industrial fermentations from the production of foods and beverages to that of valuable chemicals,such as glycerol,acetone,and later vitamins,antibiotics and alkaloids.

The unity of biology at a molecular level concept was developed when it was discovered that the carbohydrate metabolism pathways are similar in some microbes and in mammals.This discovery was made towards the end of the Pasteurization era notably by Winogradsky in Russia and Beijerinck in Holland who discovered variety of metabolic patterns by different kinds of bacteria adapted to different ecological niches.

The ecological niche is defined as 'the physical space occupied by an organism,but also its functional role in the communnity'.These organisms were isolated by using Pasteur's principle of selective cultivation:enrichment culture in which only a particular energy source is provided,and growth is restricted to those organisms that can use that source.   

SPONTANEOUS GENERATION OF ORGANISMS

The Theory of Spontaneous Generation or Abiogenesis states that the microbes arise automatically in decomposing organic matter.

 In the 17th century Francesco Redi worked out the appearance of maggots in decomposing meat dependend on  the decomposition of eggs by flies,but the idea of spontaneous generation persisted for the new world of microbes. T.Needham in 1748 experienced the appearance of organisms not present previously and concluded that these organisms appeared from the decomposition of the vegetables and meat. Later Spallanzani (1729-1799) introduced the the use of sterile culture media;he showed that infusion of meat,would remain clear indifinitely if boiled and properly sealed.

 The discovery was later on confirmed in the early 19th century,when a French confectioner,Nicholas Appert,competing for a prize by Napolean,developed the art of preserving food by  canning. In 1837, Schwann obtained similar results even when air was allowed to re-enter the cooling flask before sealing. Preliminary reports on experiments concerning alcoholic fermentation and purification were given by Schwann(1837) and Liebig(1839).

 To give more weightage, Schroder and Von Dusch applied the use of cotton plug,to exclude air borne contaminants which is still in use.

History of microbiology

In the poem, De rerum nature, Lucretious mentioned the 'seeds' of disease. India can also take pride in contributing to the development of ancient microbiology in the form of septic tanks in the Mohenjodaro and the Harappa regions .

But the existence of microbes was not established until Antony Van Leeuwenhoek could see them in simple (one-lens) microscope. Leeuwenhoek, a cloth merchant in Delft, Holland spent much of his time in grinding tiny lenses of high magnification ( 300 X or so ). He took the scurf from the root of decayed tooth and mixed it with clean rain water,and saw the mobility in animalcules. He discovered major classes of bacteria (spheres,rods and spirals),protozoa,algae,yeasts, erythrocytes, spermatozoa,and the capillary circulation. Leeuwenhoek's discoveries were described in a flow of letters to the Royal Society of London.

Aristotle (384-322BC) emphasized that animals might evolve spontaneously from the soil,plants or other unlike animals. Virgil (70-19BC) also gave opinion for the artificial propagation of bees. 

Discoveries about spontaneous generation persisted till 17 th century...