Physiological period in microbiology

Louis Pasteur's contribution to science

Louis Pasteur (1822–1895) was an eminent French scientist with a background in chemistry. Thanks to his unique experimental talent, he became the founder of several scientific fields at once: microbiology, biotechnology, disinfectology, and stereochemistry.

He began his scientific journey in chemistry. At the age of 26, Pasteur successfully defended his dissertation on arsenic compounds (potassium, sodium, and ammonia). Observing the growth of fungi, the researcher made a key discovery: microorganisms are capable of assimilating exclusively specific stereoisomers. This observation made him the father of a new science — stereochemistry.

Later, Pasteur turned to the study of fermentation processes, which at that time were dominated by Justus von Liebig's chemical theory. Pasteur experimentally proved that alcoholic, lactic acid, and acetic acid fermentations are purely biological processes. They are initiated by microorganisms and the specific enzymes they secrete. This is how modern biotechnology originated.

The scientist's most high-profile triumph was refuting the ancient dogma of spontaneous generation. For centuries, it was believed that living matter could arise from non-living matter (e.g., microbes from dirt or frogs from silt). Pasteur conducted an elegant experiment:

• He used a flask with nutrient broth equipped with a spirally curved tube (a "swan neck").
• The internal environment of the flask communicated with the surrounding air, but microbes and dust settled in the glass bends.
• As a result, the broth remained sterile, and life did not originate in it.
• However, when the tube was removed and the liquid came into direct contact with the air, the broth rapidly grew microorganisms.

In addition, Pasteur discovered for the first time the existence of anaerobiosis — the ability of bacteria to live and reproduce without access to oxygen.

Pasteurization and immunology

Studying the causes of putrefaction and so-called "diseases of wine," Pasteur proved the key role of microbes in these processes. To preserve beverages, he developed an effective method of heating liquids to 50–60 °C. This temperature treatment led to the reliable destruction of vegetative forms of bacteria.

Subsequently, this method was named pasteurization. Pasteur's work in this direction formed the basis of modern fundamental principles of asepsis and disinfection. In the field of immunology, the researcher also made a breakthrough by developing the basic principle of vaccination and the first methods for producing vaccines.

Methodology and etiology of Robert Koch

Robert Koch (1843–1910) was an outstanding German bacteriologist who revolutionized laboratory practice and research methodology. He focused on improving techniques for working with microorganisms.

Koch made a colossal contribution to the development of microbiology by proposing new methods for staining bacterial cells. He was the first to introduce microphotography into everyday practice, which made it possible to document observation results. Koch's most important achievement was the development of reliable algorithms for obtaining pure cultures of microorganisms.

Henle–Koch postulates

The concept allowing one to prove that a specific microbe is the causative agent of a particular infectious disease was originally proposed by Jakob Henle. However, Robert Koch finally formulated and developed this principle.

The postulates include three mandatory conditions:

1. The microorganism must be found exclusively in patients with the given infection and not detected in healthy individuals.
2. The causative agent must be isolated from the body as a pure culture.
3. Artificial infection of laboratory animals with this pure culture must reproduce a similar disease.

Despite its historical fundamentality, in modern clinical medicine the postulates have relative significance and are not always feasible. There are two main reasons for this:

• The impossibility of reproducing certain human diseases in animals (e.g., HIV infection).
• The phenomenon of healthy carriage, in which the pathogen is present in the body, but the clinical picture is completely absent.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Principles of vaccination and methods of vaccine production according to Pasteur
• Specifics of lactic acid, alcoholic, and acetic acid fermentation
• Methods of bacterial staining proposed by Robert Koch
• Technique for obtaining and culturing pure cultures of microorganisms

Other topics in the section "Introduction to microbiology and immunology"

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