History and Scope of Microbiology
1.1 Early History
Microbiology is the study of microbes (microorganisms), i.e., organisms too small to be observed by the naked eye, and dates back to the seventeenth century, when Hans and Zaccharias Janssen (ca. 1600) invented the first compound microscope.
Robert Hooke (1665) made early observations using a compound microscope. From his observations of cork, he coined the word “cell” to describe the “little boxes” he saw as the smallest structures of life, setting the foundation for “cell theory.”
The cell theory states that all living things are composed of cells. Anton van Leeuwenhoek (1670s and 1680s) was first to observe and describe living microbes, which he referred to as “animalcules.” His homemade microscopes magnified specimens up to 200×-300×.
Carolus Linnaeus (1735) developed a general system of classification and binomial nomenclature (genus name + specific epithet or species name).
The theory of spontaneous generation—which states that new life can arise from nonliving matter—was commonly accepted until the mid-1880s. Francesco Redi (1660s) was first to present experimental evidence to refute spontaneous generation. Redi used cloth-covered jars to show that maggots do not arise spontaneously in meat but that the meat must be open to contact with flies in order for maggots to appear. However, his results were not accepted by many (the experiment that finally put the theory of spontaneous generation to rest did not occur for another 200 years.).
John Needham (1740s) published experimental evidence in support of spontaneous generation. In his experiments, he showed that nutrient solutions could be boiled, and yet when cooled, microorganisms would soon appear. In the 1760s, Lazzaro Spallanzani countered this with experiments demonstrating that if such flasks were sealed, the microorganisms did not appear after boiling. Needham and his supporters argued that the boiling was responsible for killing some “vital force” (later thought to be oxygen upon its discovery) and that sealing the flask prevented its re-entry. It was still another hundred years before Pasteurs experiments disproved the theory.
On the medical front, Edward Jenner (1798) developed and tested the first vaccine. Jenner noticed that milkmaids exposed to cowpox rarely developed the more serious smallpox. He then used cowpox to successfully inoculate patients against smallpox.
Ignaz Philipp Semmelweis (1840s) noticed a connection between doctors doing autopsies and patients developing puerperal (childbirth) fever; he was first to suggest that doctors should wash their hands between procedures.
1.2 The Golden Age of Microbiology
The Golden Age of Microbiology (1850-1890) was a period during which major historical figures established microbiology as a viable scientific discipline.
Louis Pasteur—disproof of spontaneous generation/proof of biogenesis (1861). Pasteur devised a special kind of flask (the swan-necked flask) in order to disprove spontaneous generation. Swan-necked flasks are not sealed off; rather, the neck of the flask is open, but is long and curved. Such flasks are open to air and to any “vital force.” However, microorganisms from the outer air become trapped in the curved neck of the flask and are thus prevented from contaminating the medium.
Infusions or nutrient broths that have been sterilized by boiling do not become contaminated in such a flask unless the neck becomes broken. Thus, Pasteur disproved spontaneous generation while demonstrating that the inoculating (contaminating) organisms are present in the air.
Pasteur was first to show that microorganisms are everywhere, including the air. This discovery provided impetus for the development of aseptic techniques in the laboratory and medical situations to prevent contamination.
Pasteur was also instrumental in work on the role of yeast and other microorganisms in fermentation or the conversion of sugars to alcohol. He developed a heating process used to kill bacteria in some alcoholic beverages and milk, i.e., pasteurization.
Pasteur was also a pioneer in the area of immunology. He developed “vaccines” (he coined the term) for chicken cholera and rabies (1884). In his search for a rabies vaccine, Pasteur used the brain tissue of rabid animals to inoculate rabbits. He then used the dried spinal cords of those rabbits to inoculate experimental animals. In 1865, he used this treatment to successfully vaccinate a young boy who had been bitten by a rabid dog, and showing signs of the disease, was expected to die. The vaccine worked and the boy lived. (Modern vaccines are generally live, avirulent microorganisms, or killed pathogens or components isolated from pathogens, especially by use of recombinant DNA techniques.)
It was one of Pasteurs publications (1857) that laid the foundation for the germ theory of disease by suggesting that microorganisms are the cause of disease rather than the result of it. This theory states that microorganisms can invade other organisms and are responsible for the transmission of infectious diseases.
Joseph Lister (1860s) introduced the use of disinfectants to clean surgical dressings and instruments. Robert Kochs work (1870s) provided further support for the germ theory of disease. His work with the sheep disease anthrax was instrumental in establishing the concept of “one disease—one organism,” which is the foundation of medical microbiology.
He was the first to establish pure culture technique, and the first to use agar in growth medium. Kochs postulates (1876) are still used today as the appropriate method for demonstrating that a specific microorganism transmits a specific disease.