Classification is the process of grouping organisms. This process may be based on different features (e.g., appearance/morphology, Gram stain reaction, cell wall structure, genetic sequence, evolution). In general, these groups (or ranks) form a hierarchy from most inclusive to most exclusive:
- Domain (broadest category)
- Kingdom
- Phylum (equivalent to "Division" as used per the AMA Manual of Style3)
- Class
- Order
- Family
- Genus
- Species (individually specific category)
In medical microbiology, the species is considered the basic unit of taxonomy. Note: Occasionally, subgroups within the species are recognized; these may include subspecies. Further designations such as biotype, serotype, or genotype may be given.
Bacterial species are determined using guidelines published by the International Committee for the Systematics of Prokaryotes; definitions are now based on DNA profiling in combination with phenotypic traits. The naming of microorganisms is further established using nomenclature.
Classification is a prerequisite of identification, whereby the following questions apply: Does this microorganism belong to an established taxon? Is it something else altogether? Or something new?
3. AMA Manual of Style Committee. (2020). AMA Manual of Style - A Guide for Authors and Editors (11th ed.). Oxford University Press. https://doi.org/10.1093/jama/9780190246556.001.0001
