Classification of microorganisms in microbiology

Microbes and microorganisms: what is the difference?

In global microbiological taxonomy, it is fundamentally important to distinguish between two basic terms. The concept of "microbes" is as broad as possible—it includes absolutely all microscopic forms of life. Meanwhile, "microorganisms" is a narrower term applicable exclusively to those objects that possess a complete cellular and organismal structure.

Based on this, the microbial world is divided into two major groups:

• Acellular life forms. This includes viruses (classified into a separate kingdom Virae), as well as prions and viroids. Their main feature is the complete absence of cellular and organismal structure. This is precisely why they are classified only as microbes, but are not microorganisms.
• Cellular life forms. These are true microorganisms possessing a defined cell. They can be referred to as both microbes and microorganisms.

Classification of cellular life forms

All cellular microorganisms are divided into two major groups depending on the presence or absence of a defined cell nucleus.

1. Prokaryotes These are microorganisms that lack a defined nucleus. They include two domains:

• Domain Bacteria (Bacteria). Unites true bacteria, which are also called eubacteria.
• Domain Archaea (Archaea). This group includes ancient forms of bacteria (archaebacteria). Important medical fact: representatives of this domain do not cause diseases in humans and animals.

2. Eukaryotes These are microorganisms with a clearly defined nucleus. They are represented by one large domain — Eukarya (Eukarya), which in microbiology includes three kingdoms:

• Kingdom of protozoa (Protozoa);
• Kingdom of fungi (Eumycota);
• Kingdom of chromists (Chromista).

Principles of specialization of microbiological laboratories

To study the entire diversity of the microworld, a network of specialized laboratories has been created. Their classification is based on two main criteria: the object of study (a specific group of microbes) and the methods applied.

Specialization by studied groups of microorganisms:

• Main profiles: bacteriological, virological, mycological (studying fungi), and protozoological (studying protozoa).
• Narrow specialization: there are laboratories working only with specific taxa or groups of bacteria. These include rickettsial, chlamydial, tuberculosis, and leptospiral laboratories, as well as centers for the study of anaerobic infections.

Specialization by research methods:

• Microbiological — use classical culture methods.
• Immunological — use serological reactions.
• Molecular genetic — use PCR and other modern technologies.

It is important to note that in practice, an effective combination of various approaches is possible. For example, performing serological diagnostics can be carried out on the basis of a classical microbiological laboratory.

Class and exam questions

What else to study on this topic

• Structure, biology, ecology, and evolution of various microbial groups.
• Features of acellular life forms: viruses, prions, and viroids.
• Classical culture methods in microbiological practice.
• Molecular genetic methods (PCR) and immunological reactions.
• Specifics of work in narrow-profile laboratories (rickettsial, chlamydial, leptospiral).

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.