A type strain is a living reference lineage designated as the nomenclatural type of a species or subspecies in prokaryotic nomenclature. It consists of cultures descended from the designated strain, rather than one uniquely irreplaceable physical vial. The Code expects close agreement with the original description.[ref]
International Code of Nomenclature of Prokaryotes. Prokaryotic Code (2025 Revision) by Aharon Oren and others. Rule 18a, living cultures descended from the designated strain
This role supports comparisons between biological observations and a named reference. Culture collections preserve and identify such material; their accession identifiers can supply different labels for the same underlying type strain.[ref]
International Code of Nomenclature of Prokaryotes. Prokaryotic Code (2025 Revision) by Aharon Oren and others. Rule 18b, example of one strain with multiple collection identifiers; Rule 30(3)(b), deposition
Consider a constructed database example. Collection A labels the designated lineage A-101, while collection B labels a documented descendant B-202. Counting the two accessions as two independent species would confuse storage records with biological classification. The essential record is the documented relationship between the materials, the designated lineage and the name.
A type strain supplies a reference, not a guarantee that every other bacterial strain in the same species has identical phenotypes. It is also a living lineage whose measured properties require appropriate characterization. A comparison should state the actual material and conditions tested, so that a discrepancy can be investigated rather than silently attributed to an entire species.
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