The existence of microorganisms was hypothesized for many centuries before their actual discovery. The existence of unseen microbiological life was postulated by Jainism which is based on Mahavira’s teachings as early as 6th century BCE. Paul Dundas notes that Mahavira asserted existence of unseen microbiological creatures living in earth, water, air and fire. Jain scriptures also describe nigodas which are sub-microscopic creatures living in large clusters and having a very short life and are said to pervade each and every part of the universe, even in tissues of plants and flesh of animals. The Roman Marcus Terentius Varro made references to microbes when he warned against locating a homestead in the vicinity of swamps "because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there by cause serious diseases."[citation needed]
In the medieval Islamic world

Avicenna "ibn Sina"
At the golden age of Islamic civilization, some scientists had knowledge about Microorganisms, such as Ibn Sina in his book The Canon of MedicineIbn Zuhr "Avenzoar" who discovered Scabies Germs, and Al-Razi who spoke ofparasites in his book "The Virtuous Life" (al-Hawi).
In 1546, Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact, or vehicle transmission.

However, early claims about the existence of microorganisms were speculative, and not based on microscopic observation. Actual observation and discovery of microbes had to await the invention of the microscope in the 17th century.

Microbiology was born in 1674 when Antoni van Leeuwenhoek (16321723), a Dutch drapery merchant, peered at a drop of lake water through a carefully ground glass lens. Through this he beheld the first glimpse of the microbial world. Perhaps more than any other science, the development of microbiology depended on the invention and improvement of a tool, the microscope . Since bacteria cannot be seen individually with the unaided eye, their existence as individuals can only be known through microscopic observations. Indeed, it is interesting to speculate on how microbiology might have developed if the limits of resolution of the microscope were poorer.
Antoni van Leeuwenhoek
The practical and scientific aspects of microbiology have been closely woven from the very beginning. Perhaps it is for this reason that microbiology as a field of study did not really develop until the twentieth century. Nineteenth century "microbiologists" were chemists and physicians and a few were botanists. At that stage, the science of microbes was developing to solve very practical problems in two clear scientific fields, the science of fermentation and in medicine.
Although medicine and fermentation presented the practical problems that stimulated the development of microbiology, the first studies that put the subject on a scientific basis arose from a problem of pure science. This was the controversy over spontaneous generation. Although the crude ideas of spontaneous generation (e.g., maggots from meat) were dispelled by Francesco Redi (1626?1698?) in the seventeenth century, more subtle ideas such as that protozoa and bacteria can arise from vegetable and animal infusions, were still accepted in the nineteenth century. The controversy also involved fermentations, since it was considered that the yeast fermentation was of spontaneous origin.
Many workers became involved in the study of fermentation and spontaneous generation, but Louis Pasteur (18221895) stands out as a giant. He came into biology from the field of chemistry and was apparently able to remove all the philosophical hurdles that blocked the thinking of others. Within a period of four years after he began his studies, he had clarified the problems of spontaneous generation so well that the controversy died a natural death.
Louis Pasteur

Pasteur was also able to go easily from fermentation into the field of medical microbiology, which occupied the later part of his life. His contributions in that field were numerous, and his work in fields such as microbial attenuation and vaccination has been the basis of many modern medical practices. It should be emphasized that the development of sterilization methods by researchers such as Pasteur and John Tyndall (18201893), so necessary to the solution of the spontaneous generation controversy, were essential to put the science of microbiology on a firm foundation. The workers did not set out to develop these methods, but they evolved as a bonus that was received for solving the spontaneous generation question.
Other important developments were in medicine. The microbiological aspects of medicine arose out of considerations of the nature of contagious disease. Although the phenomenon of contagion, especially with respect to diseases such as smallpox , was recognized far back in antiquity, its nature and relationship to microorganisms was not under-stood. It was probably the introduction of syphilis into Europe, which served to crystallize thinking as here was a disease that could only be transmitted by contact and helped to formulate the question, what is being transmitted? Gerolamo Fracastoro (14781553) gave syphilis its name in the sixteenth century and came close to devising a germ theory of disease , an idea that later attracted a number of workers all the way down to the nineteenth century. By the late 1830s, Schwann and Cagniard-Latour had shown that alcoholic fermentation and putrefaction were due to living, organized beings. If one accepted the fact that the decomposition of organic materials was due to living organisms, it was only a step further to reason that disease, which in many ways appears as the decomposition of body tissues, was due to living agents. Jacob Henle, in 1840, further commented on this similarity and with the newfound knowledge on the nature of fermentation, he proceeded to draw rather clear conclusions also saying that experimental proof would be required to clinch this hypothesis. That evidence came later from Robert Koch provided, in 1867, the final evidence proving the germ theory. He established the etiologic role of bacteria in anthrax and as a result proposed a set of rules to be followed in the establishment of etiology. The key to Koch's observation was the isolation of the organism in pure culture . While limiting dilutions could have been used (as described previously by Joseph Lister , 18271912), Koch promoted the use of solid media, giving rise to separate colonies and the use of stains. In 1882, Koch identified the tubercle bacillus and so formalized the criteria of Henle for distinguishing causative pathogenic microbes. This set of criteria is known as Koch's postulates .
Robert Koch

One of the most important applied developments in microbiology was in understanding the nature of specific acquired immunity to disease. That such immunity was possible was known for a long time, and the knowledge finally crystallized with the prophylactic treatment for smallpox introduced by Edward Jenner (17491823). Using cowpox , Jenner introduced the first vaccination procedures in 1796. This occurred long before the germ theory of disease had been established. Later workers developed additional methods of increasing the immunity of an individual to disease, but the most dramatic triumph was the discovery of the diphtheria and tetanus antitoxins by von Behring and Kitisato in the 1890s. This work later developed into a practical tool by Paul Ehrlich(18541915) and it was now possible to cure a person suffering from these diseases by injecting some antitoxic serum prepared by earlier immunizationof a horse or other large animal. This led for the first time to rational cures for infectious diseases, and was responsible for Ehrlich's later conception ofchemotherapy . The antibiotics era, which followed the groundbreaking work of Alexander Fleming (18811955) with penicillin , was another important step in the understanding of microbiology.

Alexander Fleming
Most of the most recent work in the development of microbiology has been in the field of microbial genetics and how it evolved into a separate discipline known as molecular biology . This work really began in the 1940s, whenOswald Avery, Colin MacLeod and Maclyn McCarty demonstrated that the transforming principle in bacteria, previously observed by Frederick Griffiths in 1928, was DNA . Joshua Lederberg and Edward Tatum demonstrated that DNA could be transferred from one bacterium to another in 1944. With the determination of the structure of DNA in 1953, a new and practical aspect of microbiology suddenly became realised, and the foundations of genetic engineering were laid. It is perhaps important to realize that if it were not for bacteria and their characteristics, genetic engineering would not be possible. The concept of DNA transfer was essentially born in the 1940s. Later on, in the late 1960s bacterial restriction enzymes were discovered and the possibilities of splicing and rearranging DNA emerged. The advances in molecular biology following these major breakthroughs have been immense but it is important to realize that the field of microbiology lies at their root.


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