= Type strain
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 (biology)>, rather than one uniquely irreplaceable physical vial. The Code expects close agreement with the original description.<International Code of Nomenclature of Prokaryotes. Prokaryotic Code (2025 Revision) by Aharon Oren and others>[Rule 18a, living cultures descended from the designated strain]{ref}
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>.<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]{ref}
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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