Definition and scope of microbiology

Summary

Microbiology is the scientific study of microorganisms (microbes), which can be unicellular, multicellular, or acellular. It includes a wide range of sub-disciplines such as virology, bacteriology, protistology, mycology, immunology, and parasitology. Microbes are commonly grouped as prokaryotes or eukaryotes: eukaryotic microorganisms have membrane-bound organelles (including fungi and protists), while prokaryotes are conventionally described as lacking membrane-bound organelles (including Bacteria and Archaea). The scope of microbiology extends beyond traditional laboratory methods. Historically, microbiologists relied on culture, staining, and microscopy to isolate and identify microbes, but only a small fraction of environmental microbes can be cultured in isolation. Modern microbiology therefore also uses molecular biology tools—such as DNA sequence-based identification (e.g., 16S rRNA gene sequencing for bacteria)—to detect and classify microbes that are difficult or impossible to culture. The field also addresses organisms at the boundaries of “microbe” definitions, such as viruses (sometimes classified as organisms) and prions (not considered microorganisms but studied in relation to infectious disease).

Key Points

• 1

  Microbiology studies microorganisms, including unicellular, multicellular, and acellular forms.

• 2

  Microbes are typically classified as prokaryotes (Bacteria, Archaea) or eukaryotes (fungi, protists).

• 3

  The field includes many sub-disciplines such as virology, bacteriology, mycology, immunology, and parasitology.

• 4

  Microbiology’s scope has expanded from culture/microscopy to molecular identification methods because most microbes cannot be cultured.

• 5

  Microbiology also engages with borderline infectious agents such as viruses and prions, even when definitions differ.