The place of genetics and mycology in microbiology
Microbiological science has a clear internal structure and is divided according to the objects and methods of research. Genetics is part of general microbiology along with morphology, physiology, biochemistry, ecology, and evolution. It studies the fundamental patterns of hereditary information transfer in microorganisms.
The study of fungi themselves is the focus of mycology, a vital branch of specialized microbiology. In modern laboratory and clinical practice, these two fields are closely intertwined. Mycological laboratories specialize exclusively in fungi, yet they utilize a wide arsenal of technologies, including genetic ones, for their study.
Molecular genetic methods in the diagnosis of mycoses
The specialization of modern laboratories is based on two main criteria: the group of microbes under study and the methods applied. In the diagnosis of fungal infections, classical culture, immunological (serological reactions), and molecular genetic methods (primarily PCR) are used.
There is a strict rule when working with clinical material: if molecular genetic, microscopic, and culture examinations are ordered for a patient, all of them must be performed in parallel and strictly from the same sample of diagnostic material. This is critically important for the accurate genetic identification of the pathogen and the elimination of errors.
A comprehensive approach to fungal identification
Indications for in-depth mycological examination include suspected fungal lesions of the lungs and the need to monitor the efficacy of antifungal therapy.
The following diagnostic material is used for fungal DNA isolation and cultivation:
- Sputum.
- Bronchial washings.
- Bronchoalveolar lavage (BAL).
- Biopsy specimens and surgical material.
In addition to genetic tests, precise identification utilizes inoculation onto specialized Sabouraud dextrose agar (Emmons modification), as well as direct and fluorescent microscopy with Calcofluor White staining. To increase the diagnostic yield, the material (BAL, aspirate) must be centrifuged and treated with mucolytics.
Genetic and evolutionary aspects of parasitism
Many fungi are parasites. Parasitism is a form of biotic interaction in which the parasite uses the host as a source of nutrition or habitat while causing a certain amount of harm. This interaction is directly relevant to population genetics.
Infections are most severe in patients with hereditary immune defects or a predisposition to allergic reactions. A prime example is allergic bronchopulmonary aspergillosis (ABPA). Notably, standard microscopy and sputum culture detect Aspergillus spp. fungal colonization in only 20–60% of such patients, necessitating the use of more sensitive methods.
From an evolutionary perspective, the death of susceptible individuals removes alleles that reduce viability from the population's gene pool. Thus, parasitic fungi have a beneficial effect on the genetic structure of the host population, regulate population numbers, and promote the stability of biogeocenoses.
The SINGLE-sample rule: genetics (PCR), microscopy, and culture are performed strictly in parallel from a single biomaterial container to avoid discrepancies in results.
Class and exam questions
What methods are used for the genetic diagnosis of fungi?
The main molecular genetic method is the polymerase chain reaction (PCR). It is used in combination with classical culture and microscopic examinations.
How to properly collect material for a comprehensive mycological examination?
The main rule is that molecular genetic, microscopic, and culture examinations must be performed in parallel strictly from the same sample of diagnostic material.
How do parasitic fungi affect the genetics of the host population?
By causing the death of individuals with hereditary defects and weak immunity, parasites remove alleles that reduce viability from the gene pool. This stabilizes the genetic structure of the population.
Do classical methods always detect fungi in allergic bronchopulmonary aspergillosis?
No, microscopy and sputum culture detect Aspergillus spp. colonization in only 20–60% of patients with ABPA, which highlights the importance of comprehensive diagnostics.
What else to study on this topic
- Classification of microbiological laboratories by objects and methods
- Ecological microbiology and the role of microbes in biogeocenoses
- Culture methods: features of Sabouraud media
- Algorithms for identifying challenging pathogens and nontuberculous mycobacteria
- Medical parasitology: classification and impact on the gene pool
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