GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

1. EMERGENCE AND DEVELOPMENT OF MICROBIOLOGY

1.2. THE ECOLOGICAL AND PHYSIOLOGICAL PERIOD IN THE DEVELOPMENT OF MICROBIOLOGY. LOUIS PASTEUR'S DISCOVERIES

This stage in The Development of microbiology begins In the second half of the 19th century with the scientific discoveries of the French scientist Louis Pasteur (1822–1895). The establishment of MICROBIOLOGY AS A science is intrinsically linked to his name. The principal discoveries of L. Pasteur are outlined below.

The Role of Microorganisms in the chemical Transformation of substances. L. Pasteur demonstrated that a mixture of sodium and ammonium tartrate salts forms Two Types of crystals that are isomers. Solutions of one crystal type rotate the plane of a polarized light beam exclusively to the right, whereas the other rotates it to the left. Through these investigations, L. Pasteur discovered that a mold fungus growing in a solution of tartaric acid is capable of metabolizing only the right-handed crystals. Consequently, it was concluded for the first time that microorganisms can drive Chemical transformations of Organic compounds and that There is a rather narrow specialization of microorganisms regarding nutrient substrates.

Fermentation. In the first half of the 19th century, the French botanist C. Cagniard de LaTour, while investigating the sediment formed As a result of Alcoholic Fermentation, detected living microorganisms in it. Independently of one another, German naturalists T. Schwann and F. Kützing, while examining the pellicle formed during acetic acid fermentation and the sediment produced during alcoholic fermentation, also discovered microorganisms. The scientists concluded that the processes of acetic acid and alcoholic fermentation are driven by microbes. However, this Conclusion did not receive due recognition at the time, as The Theory of the physicochemical nature of fermentation—advocated by prominent chemists such as J. Liebig and J. Berzelius—was more popular.

In 1856, L. Pasteur commenced his study of fermentation processes, which he investigated over a period of 20 years. He established that specific Types of fermentation, resulting in The formation of different products, are caused by distinct species of microorganisms. For instance, alcoholic fermentation (The conversion of sugar into alcohol) is driven by Yeasts, whereas Lactic acid fermentation (the conversion of sugar into lactic acid) is caused by rod-shaped Bacteria.

Anaerobiosis. In 1857, L. Pasteur discovered that air inhibits the growth of the agents responsible for Butyric acid fermentation. Specifically, in the presence of air, these organisms became motile-inactive [immotile], and bubbling air through the fermentation medium halted butyric acid fermentation altogether. Thus, it was concluded for the first time that microorganisms exist which can thrive exclusively under oxygen-free conditions. L. Pasteur introduced the terms aerobic and anaerobic to designate microorganisms that live in the presence or absence of oxygen, respectively. Furthermore, L. Pasteur was the first to conclude that yeasts are facultative anaerobes, meaning they are capable of surviving under both aerobic and anaerobic conditions.

Structure/149.html">The problem of spontaneous generation. Ancient scholars believed that small animals originate from non-living matter. The idea of such spontaneous origin of life remained popular even in the Middle Ages. In the mid-18th century, the Italian scientist Lazzaro Spallanzani concluded that the spoiling of organic solutions is caused by microorganisms entering them from the air.

L. Pasteur demonstrated the ubiquitous presence of microorganisms in the air and its sterility after high-Temperature heating. Through simple experiments, he proved that spontaneous generation in sterilized organic extracts does not occur under either oxygen-free or oxygen-rich conditions.

The English scientist J. Tyndall established that, unlike vegetable and meat infusions, hay infusion undergoes Microbial growth after being heated. This led to the conclusion that bacteria exist in dried hay in two forms: thermolabile (which are killed by boiling) and thermostable (which withstand boiling).

German botanist F. Cohn discovered that hay contains the hay bacillus, which forms spores capable of surviving boiling for several hours. This marked the discovery of sporulation in bacteria. Building upon this, J. Tyndall developed a sterilization method based on repeated heating at intervals sufficient for spores to germinate into the thermolabile vegetative form of bacteria. This method became known as tyndallization.

Microbes as causative agents of disease (1865–1868). While investigating the causes of wine and beer spoilage during their production and storage, L. Pasteur established that the souring and bittering of these beverages are caused by contaminant microorganisms that proliferate during fermentation or in the finished products. He termed such spoilage the "diseases" of wine and beer and proposed Methods to prevent them (heating the finished product). Later, L. Pasteur established that puerperal fever is caused by streptococci, discovered the causative agents of Osteomyelitis, purulent abscesses, and fowl cholera, and concluded that every infectious disease is caused by a specific microorganism.

Building on L. Pasteur's research, the English surgeon J. Lister concluded that the suppuration of surgical wounds results from microbes entering the wound from the air during surgery. J. Lister was the pioneer who proposed treating surgical instruments with carbolic acid and spraying carbolic acid into the air of operating rooms. This method was termed antisepsis, which was later complemented by the term asepsis—referring to the disinfection of all objects coming into contact with a wound.

Microbial attenuation. In L. Pasteur's experiments on fowl cholera, an old culture of the disease agent was used to infect chickens. It turned out that all the chickens in this experimental series survived (whereas previously half of them would have died). Moreover, upon subsequent re-infection with a fresh culture, all these same chickens remained alive. L. Pasteur concluded that in an aged culture, the pathogenic properties of microorganisms diminish while their ability to enhance resistance against the pathogen is preserved. Based on these observations, L. Pasteur proposed METABOLISM/2.html">THE CONCEPT OF attenuation (the weakening of virulence) of pathogenic microorganisms for the purpose of preventing infectious diseases. L. Pasteur named such preparations Vaccines. He produced vaccines against fowl cholera and bovine anthrax. By establishing the principles of vaccine manufacturing and the methods of preventive vaccination, L. Pasteur laid the foundations of the science of immunology.