Microbiology often has been defined as the study of organisms and agents too small to be seen clearly by the unaided eye- i.e., the study of microorganisms. Because objects less than one about one millimeter in diameter cannot be seen clearly and must be examined with a microscope, microbiology is concerned primarily with organisms and agents this small or smaller. Its subjects are viruses, bacteria, many algae and fungi, and protozoa. Yet other members of this group particularly some of the algae and fungi are large and quite visible. Two bacteria that are visible without a microscope Thiomargarita and Epulopiscium, also have been discovered. The difficulty in setting the boundaries of microbiology led Roger Stanier to suggest that the field be defined not only in term of size of its subject but also in terms of its technique. Microbiology employs techniques such as sterilization and the use of culture media that are necessary for successful isolation and growth of microorganisms.
The Discovery of Microorganisms
The Roman philosopher Lucretius and the physician Girolamo Fracastoro suggested that disease was caused by invisible living creatures. The fist person to observe and describe microorganisms accurately was the amateur microscopist Antony vas Leeuwenhoek (1632-1723).
From the earliest times people had believed in spontaneous generation that living organism could develop from nonliving matter. Leeuwenhoek�s discovery of microorganisms renewed the controversy. In 1748 the English Priest John Needham reported the results of his experiments on spontaneous generation. Needham boiled mutton broth and then tightly stopped the flasks. Eventually many of the flasks become cloudy and contained microorganisms. He thought organic matter contained a vital force that could confer the properties of life on non living matter. Italian priest (1729-1799) improved on Needham�s experimental design by first sealing the glass flasks that contained water and seeds. If the sealed flasks were placed in boiling water for � of an hour, no growth took place as long as the flask remained sealed. He proposed that air carried germs to the culture medium, and also commented that the external air might be required for growth of animals already in the medium.
The role of microorganisms in Disease
The importance of microorganisms in disease was not immediate to scientist and it took many years to establish connection between microorganisms and illness. The first direct demonstration of the role of bacteria in causing disease came from the study of anthrax by the German physician Robert Koch (1843-1910).
The Scope and Relevance of Microbiology
As the scientist write Steven Jay Gould emphasized, we live in the Age of Bacteria. They were the first living organisms on our planet, live virtually everywhere life is possible, are more numerous than any other kind of organism and probably constitute the largest component of earth�s biomass. The whole ecosystem depends on their activities and they influence the human society in countless ways. Thus modern microbiology is large discipline with many different specialties; it has great impact on fields such as medicine, agriculture and food sciences, ecology, genetics, biochemistry and molecular biology.
One indication of the importance of microbiology in the 20th century is the Nobel Prize given for work in physiology or medicine. About 1/3 of these have been awarded to scientist working on microbiological problems.
Microbiology has both basic and applied aspects. Many microbiologist are interested primarily in the biology of the microorganism themselves. Others are interested in microbial morphology or particular functional processes or work in field such as microbial genetics and molecular biology. Many have more applied orientation and work on practical problems in fields such as medical microbiology, food and dairy microbiology, and public health microbiology.
