Тоpic 1. Morphology of microorganisms
1.1. History of microbiology. The basic scientists and their advances
Heuristic stage (4th–3rd Millennium BC — 16th century AD) is associated rather with the logical and methodological techniques to finding the truth, i.e., heuristics, than with any experiments and evidence. However, the proof of the existence of invisible pathogens became possible after the invention of the microscope. The priority in the discovery of microorganisms owned by a Dutch amateur-naturalist Antonie van Leeuwenhoek. Studying under the microscope of various objects (water, infusions, plaque, blood, stool, semen), A. Leeuwenhoek observed tiny animals, which he called animalcules. A. Leeuwenhoek regularly reported his observations in the Royal Society, and in 1695 summarized in the book «Arcana naturae detecta» (Nature’s mysteries disclosed). Thus, with the invention of the microscope A. Leeuwenhoek begins the next stage in the development of microbiology, called morphological.
Morphological stage. Although the emergence of disease was associated with the now exposed microorganisms, it is necessary, however, to have direct evidence. The method of origin and reproduction of microorganisms was discovered by the eminent French scientist Louis Pasteur, who through a clever and brilliantly simple experiment demonstrated that spontaneous generation does not exist. The rapid development of microbiology in the 19th century led to the discovery of the causative agents of many infectious diseases (anthrax, plague, tetanus, diphtheria, dysentery, cholera, tuberculosis, etc.).
Physiological period. The discovery of new microorganisms was accompanied by the study of not only their structure, but also their life. This stage is associated with the name of Louis Pasteur, the founder of medical microbiology, immunology, and biotechnology. A well-rounded and educated individual, a brilliant experimenter, and a member of the French Academy of Sciences and the French Academy of Medicine, Pasteur made a series of remarkable discoveries. Over a short period from 1857 to 1885, he demonstrated that fermentation (lactic acid, alcoholic, and acetic) is a chemical process triggered by microorganisms; he disproved the theory of spontaneous generation; and he discovered the phenomenon of anaerobiosis, i.e., the ability of microorganisms to live in the absence of oxygen.
The physiological period in the development of microbiology is also associated with the name of the German scientist Robert Koch, who developed methods for obtaining pure bacterial cultures, staining bacteria for microscopy, and microphotography. Koch is also known for formulating Koch’s postulates, which are still used today to establish the causative agent of a disease.
Paul Ehrlich, a German chemist, proposed the humoral theory (from Latin humor — liquid) of immunity. He believed that the immune system triggers the formation of antibodies that neutralize toxins. This was proven by the discovery of antitoxins — antibodies that neutralize toxins in animals that were administered diphtheria or tetanus toxin (by Emil von Behring and Shibasaburo Kitasato).
However, the research of Elie Metchnikoff (1845–1916) showed that specialized cells, macrophages and microphages, play a significant role in the formation of the immune system. These cells engulf and digest foreign particles including bacteria. Metchnikoff’s research on phagocytosis convincingly demonstrated that in addition to humoral immunity, there is cellular immunity.
Elie Metchnikoff, a close colleague and follower of Louis Pasteur, is rightfully considered one of the founders of immunology. His work laid the foundation for the study of immunocompetent cells as the morphological basis of the immune system, its unity, and biological essence.
Immunological period was characterized by the discovery of the fundamental reactions of the immune system to genetically foreign substances (antigens): antibody formation, delayed-type hypersensitivity (DTH), immediate-type hypersensitivity (ITH), tolerance, and immunological memory. DTH and ITH are two reactions at the root of allergies (from the Greek allos — other and ergon — action), i.e., diseases characterized by certain clinical symptoms caused by aberrant reactions to an antigen. Allergic reactions can occur, for example, to serum products, antibiotics, animal and plant proteins, house dust, feathers, fur, etc.
In 1911, Russian doctor M. Raisky observed for the first time the «phenomenon of long-term revaccination» (immunological memory), i.e., the rapid, energetic formation of antibodies upon repeated introduction of the same antigen. Subsequently, F. Burnet linked this to the formation of memory cells — T-lymphocytes — after the primary encounter with an antigen.