Introduction to symbiotic relationships
The relationships between macro- and microorganisms in nature are described by the general biological concept of symbiosis. In pathophysiological terms, three main types of such relationships are distinguished, which are determined by the nature of the microbe's effect on the host organism. These forms include parasitism, mutualism, and commensalism. Each form is characterized by a specific category of participating microorganisms and specific consequences for the macro-organism. Understanding these basic differences is fundamental to studying any infectious processes.
Characteristics of main forms of symbiosis
- Parasitism
This type of relationship represents a pronounced form of antagonism. The microbes involved here are exclusively pathogenic categories of pathogens. In parasitism, the microorganism purposefully uses the macro-organism (its host) as a necessary source of nutrition and as a habitat. This habitat can be either permanent or temporary for the pathogen. The main effect of parasitism is that microbes cause direct harm to the host. Often, this damaging effect is realized through the production of various toxins by the pathogens.
- Mutualism
Unlike parasitism, this is an absolutely mutually beneficial coexistence of two organisms. Non-pathogenic categories of microbes participate in mutualism. A classic example of such harmonious interaction is the bacteria of the normal intestinal microflora, which receive the necessary living conditions from the macro-organism while providing it with a certain benefit in return.
- Commensalism
Considered by specialists to be an intermediate type of relationship. Opportunistic microorganisms participate in this process. The essence of commensalism is that microbes successfully multiply within the macro-organism without causing any harm to it (provided that normal host living conditions are maintained). The main localization of such microorganisms is the normal microflora of the intestine, skin integuments, and various mucous membranes.
Types of infectious disease pathogens
The development of an infectious process is directly related to the introduction of a specific agent. The main groups of infectious disease pathogens include the following:
- Protozoa
- Fungi
- Bacteria
- Viruses
- Prions
Each of the listed groups has its own biological characteristics that determine the subsequent scenario of interaction with the host body.
Features of the development of the infectious process
The infectious process is not a universal template phenomenon. Its specific features and mechanisms of development strictly depend on the nature of the specific microorganism that caused the disease.
- Bacterial infections. In pathological physiology, they represent the classic model of the infectious process. Using bacterial agents as an example, the standard stages of interaction between the pathogen and the macro-organism are studied.
- Viral infections. They have very significant differences from the classical bacterial model. The main reason for these differences lies in the very nature of viruses: they are genome parasites. This means that the viral infectious process proceeds according to different laws, fundamentally differing from the bacterial one.
Briefly: answers to topical questions
Through which factors is the damaging effect of causative bacteria realized during parasitism?
The damaging effect of bacteria during parasitism is realized through the production of toxins and enzymes, as well as adhesion and invasion factors. The main pathogenicity factors include:
- Morphological structures (e.g., a capsule that ensures adhesion and protects against phagocytosis).
- Aggressive enzymes (hyaluronidase, plasmocoagulase, fibrinolysin, lipase, protease, neuraminidase).
- Toxins (exotoxins and endotoxins causing intoxication and cell damage).
Which specific bacteria constitute the normal intestinal microflora during mutualism?
The normal microflora of the large intestine includes the following bacteria: the main group — bifidobacteria, bacteroides; the accompanying group — lactobacilli, escherichia, enterococci; the residual group — citrobacter, enterobacter, proteus, clostridia, staphylococci.
Under what conditions do opportunistic microorganisms (commensals) begin to harm the macro-organism?
Opportunistic microorganisms begin to harm the macro-organism under a combination of the following conditions:
- Decreased immunobiological properties (resistance) of the macro-organism (e.g., in secondary immunodeficiency against the background of HIV, diabetes mellitus, leukopenia, ischemia, tissue damage).
- Increased virulence of the microorganisms themselves.
- Introduction of the pathogen from natural habitats into sterile zones (e.g., in aspiration pneumonia).
What is the mechanism of development of the infectious process during prion infection?
The mechanism of prion infection development is associated with the penetration of the pathological prion (PrP-Sc) into the body. Once inside, the infectious agent undergoes primary accumulation and partial replication in the cells of the lymphoreticular system (B-cell zones of the tonsils, thymus, lymph nodes, spleen). Then, prions spread along nerves from organs of immunogenesis to the nearest axons, where significant replication occurs. Upon reaching a critical concentration, PrP-Sc moves into the spinal cord and then into the brain, causing dysproteinosis, spongiform changes, neuronal degeneration, and gliosis.
Which types of pathogenic protozoa are frequent causative agents of human infectious diseases?
Pathogenic protozoa and closely related groups sources for humans include: amoebae — Entamoeba histolytica; flagellates — trichomonads, leishmania, trypanosomes; Sporozoa — causative agents of malaria, toxoplasmosis, and babesiosis; ciliates — Balantidium coli; in the kingdom Chromista — Blastocystis hominis. Malaria is called the most common protozoan infection; its main causative agents are Plasmodium falciparum, P. vivax, P. ovale, P. malariae. Among protozoan/parasitic causes of chronic colitis, amoebae, giardia, trichomonads, and balantidia are also indicated.
For quick memorization of symbiosis forms, use the association: Parasitism — pathogens cause damage; Mutualism — peaceful and mutually beneficial coexistence; Commensalism — lodgership of opportunistic flora without harm to the host.
Class and exam questions
Which microorganisms participate in commensalism and where do they inhabit?
Opportunistic microorganisms participate in commensalism. Under normal conditions, they are localized as part of the normal intestinal microflora, on the skin and mucous membranes, without harming the macroorganism.
What is the essence of parasitism as a form of symbiosis?
Parasitism is a form of antagonism in which a pathogenic microbe uses the host as a source of nutrition and a permanent or temporary habitat. This interaction always harms the macro-organism, often due to the production of toxins.
Why are viral infections considered separately from bacterial ones?
Bacterial infections serve as a classic model of the infectious process. Viral infections, however, have significant differences, since viruses by their nature are genome parasites, which changes the mechanics of their interaction with the cell.
What else to study on this topic
- Mechanisms of toxin production by pathogenic microorganisms during parasitism
- Conditions for the transition of opportunistic flora into pathogenic flora during commensalism
- Differences between temporary and permanent habitats of pathogens
- Genome parasitism: specifics of viral infection development
- The role of normal intestinal microflora bacteria in mutualism
Master the entire topic in the "Pathophysiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Relationships of macro- and microorganisms" and 4,913 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 135 video lessons on the subject
Other topics in "Chapter 7. Infectious Process"
Free video lessons: pathophysiologyShort lessons with lecture notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.