ECOLOGICAL BIOCHEMISTRY - Study Guide - V. M. Isaenko 2005

Chapter 2. ECOLOGICAL AND BIOCHEMICAL INTERACTIONS OF PROKARYOTES, MICROSCOPIC FUNGI, AND ALGAE WITH HIGHER PLANTS AND ANIMALS

2.1. General Concepts of Microbial Pathogenicity

Clarifying The Role of Microorganisms in the onset of various diseases and their identification have paved the way for uncovering The Nature of infectious diseases. Microorganisms capable of causing diseases are termed pathogenic, or disease-causing.

According to one evolutionary hypothesis regarding microorganisms, Symbiosis in the form of parasitism gave rise to pathogenic microorganisms, which subsequently differentiated into obligate parasites, necroparasites, and toxigenic Saprophytes.

It is widely believed that pathogenic microorganisms may originate from saprophytes upon acquiring virulence Plasmids. Consequently, alterations in genetic material led to The Emergence of diverse microbial species, including pathogens that under certain conditions cause various diseases in humans, animals, and plants.

During their evolutionary development, pathogenic microorganisms adapted to a parasitic mode of Nutrition within the Tissues and fluids of the host Organism. The infected organism responds to pathogen invasion through specific reactions manifested as disease symptoms and various protective adaptations.

Alongside pathogenic microorganisms, there are so-called opportunistic microorganisms that form part of the normal microflora of animals and humans. Therefore, the outcome of pathogen entry depends not only on the reactivity of the organism but also on the composition of its normal microflora, which can exert either antagonistic or synergistic effects.

Pathogenic microorganisms include numerous representatives of Bacteria, Fungi, Mycoplasmas, rickettsiae, Viruses, and Protozoa. Pathogenicity is a species-specific trait characterizing the ability of microorganisms to cause infectious diseases. In other words, it is a complex of disease-causing properties acquired by a given microorganism in the Struggle for Existence and ADAPTATION TO A parasitic lifestyle.

Pathogenic microorganisms are characterized by their Specificity. Each representative of different pathogenic species can induce a specific disease with unique, characteristic symptoms. Infection specificity is an important feature manifested in the selectivity of Tissue and organ involvement, pathogen localization, and Clinical presentation. Pathogenicity is determined by virulence, aggressiveness, and toxigenicity.

Virulence refers to the degree of pathogenicity of a given microbial culture (strain). While pathogenicity is a constant species trait, virulence is an individual property that can change under the Influence of Environmental factors (light, Temperature, humidity, etc.). Virulence can be enhanced or attenuated through passage in susceptible laboratory animals, transformation, Transduction, Treatment with antimicrobial agents, or successive subculturing on nutrient media.

Aggressiveness is the ability of microorganisms to invade an organism, establish themselves, multiply, and spread. The material basis of aggressiveness includes invasiveness factors, aggressins, and Polysaccharides. Invasiveness or spreading factors comprise a range of Enzymes produced by microorganisms that facilitate entry and dissemination within the host.

Bacterial capsule and Cell polysaccharides (e.g., in streptococci) inhibit phagocytosis and, together with aggressins, promote the establishment and proliferation of microorganisms within the infected host.

The pathogenicity of the vast majority of microorganisms is primarily based on their toxigenicity—The ability to produce toxins, which are chemically diverse substances capable of causing specific disorders and even death of the infected organism. Based on their production mode, toxins are divided into exotoxins and endotoxins.

Exotoxins are poisonous substances released into the environment by microbial Cells as metabolic products. As a rule, they are simple Proteins characterized by pronounced toxicity, meaning they exert toxic effects on susceptible organisms at extremely low doses. Exotoxins exhibit selectivity, which is the ability to affect specific tissues and Organs. For example, diphtheria exotoxin targets the Adrenal Glands and Heart Muscle, whereas tetanus exotoxin affects motor Nerve Cells. They are sensitive to high temperatures, light, and oxygen, and are rapidly destroyed by boiling.

Endotoxins are compounds typically associated with specific microbial structures and released only upon cell autolysis. Chemically, they are far more complex than exotoxins, containing proteins, Lipids, and polysaccharides. These toxins are lipopolysaccharide-Structure/178.html">Protein Complexes derived from The Cell walls of Gram-negative bacteria.

It is worth noting that many non-toxigenic microorganisms grow and multiply within the host organism just as successfully as toxigenic ones. Therefore, toxin production is not an obligatory characteristic of microorganisms.

The interaction between a susceptible organism and a pathogenic microorganism under specific environmental conditions is termed an infectious process. Infection refers to the complex biological processes that occur in organisms As a result of the action of disease-causing pathogens. Biologically, the infectious process represents a form of parasitism.

Infectious diseases are classified as exogenous or endogenous. In exogenous infections, the pathogen enters the body from the external environment—from sick individuals, carriers, or via contaminated food, Water, air, soil, or objects. Endogenous diseases (autoinfections) arise from the activation of the host's resident microflora, which can occur due to disruptions in internal Homeostasis or external environmental influences.

A complex struggle unfolds between the host organism and the invading microorganisms. If the organism fails to resist the pathogens and neutralize their harmful effects, and if environmental conditions favor Microbial growth, an infectious disease develops.

Consequently, the onset and development of an infectious process require three core components: 1) the presence of a pathogenic microorganism; 2) its entry into a susceptible organism; and 3) specific environmental conditions governing the interaction between the microbe and the infected host.

The physiological state of the organism is of critical importance for The Development of an infectious process. The degree of its involvement depends on species and genotype, reactivity, Central Nervous system disorders, Protein deficiency, vitamin and hormone status, and other factors. Depending on the state of the organism and environmental influences, the infectious process may culminate in the elimination of the pathogen, the death of the host, or the establishment of mutual adaptation between them.

Microbial invasion does not always result in disease; in many cases, it is limited to a brief, asymptomatic infection or a relatively prolonged carrier state.

Microorganisms exhibit specific species resistance. For instance, humans are susceptible to Meningococcal meningitis, whereas nearly all animals are resistant to it. Another example of genotypic resistance is the Immunity of Algerian sheep to the anthrax bacillus, which affects most other herbivores.

The capacity of organisms to neutralize pathogens is closely linked to environmental conditions, lifestyle, underlying health status, diet, and age-related characteristics.