25 topics with concise breakdowns: definitions, key facts, and class questions.
This section is the morphological foundation of microbiology. It compiles essential knowledge on the appearance, structure, and categorization of microorganisms. We provide a detailed breakdown of the classification of all major infectious agents: bacteria (including spirochetes, actinomycetes, rickettsiae, chlamydiae, and mycoplasmas), microscopic fungi (zygomycetes, ascomycetes, deuteromycetes), protozoa, viruses, and prions.
The central part of the section focuses on the structure of the bacterial cell. You will study its structures sequentially: the cytoplasmic membrane, nucleoid, and plasmids, as well as additional virulence and defense elements—capsules, flagella, pili, and bacterial spores. Viral morphology and structure are also covered in a dedicated subsection.
In practical classes and examinations, the strictest scrutiny is traditionally applied to cell wall structure (particularly the cell wall of Gram-negative bacteria) and Gram staining. This is not just dry theory, but the foundation for understanding antibiotic action in your future clinical practice. I advise paying maximum attention to these articles.
What is the difference between classification and taxonomy?
Classification is the actual distribution of microbes into groups, whereas taxonomy is the theoretical framework and set of rules governing this distribution.
Why do cocci form different clusters (chains, grape-like clusters, packets)?
The shape of clusters directly depends on the number of planes in which cell division occurs and whether physical connection between cells is maintained after division.
What is the main difference between spirochetes and other coiled bacteria (spirilla, helicobacters)?
In the arrangement of flagella. In spirochetes, flagella (periplasmic fibrils) are located inside the cell — between the protoplasmic cylinder and the outer membrane, whereas in other bacteria such as Proteobacteria, they emerge into the surrounding environment.
What are drusen and where are they found?
Drusen (or "sulfur" granules) are dense colonies of actinomycetes in affected tissues and pus. Under the microscope, they look like a tangle of intertwined filaments with radially extending rays ending in club-shaped thickenings.
Can rickettsiae be grown on blood agar?
No, rickettsiae are obligate intracellular parasites. Their growth requires living target cells (tissue cultures, chicken embryos, or animals).
Why do chlamydiae fail to grow on simple nutrient media?
Due to energy parasitism and the inability to synthesize their own ATP, they can only replicate inside living cells. Laboratories use chicken embryos, laboratory animals, or special cell lines (HeLa, McCoy).
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