Reference strains: traceability and laboratory management

A reference strain supports a control only when its identity, provenance and fitness for use are known. The initial certificate is one point in the chain: it does not automatically describe every subsequent laboratory operation.

The management task is to trace a test back to the material actually used and, in the other direction, identify tests dependent on a problematic reference. This article develops that documentary chain without propagation instructions or cultivation conditions.

1. Define what the reference must demonstrate

A reference strain has a documented origin and characteristics. A control material checks a defined property within the test system. An in-house isolate instead comes from a sample or the local environment: it may have a justified role, but it does not automatically replace the reference required by the method.

Match selection to the function: medium performance, method suitability, identification control or another specific check. An expected response in one application does not demonstrate every characteristic needed in another. A growth promotion test control therefore needs a rationale distinct from verification of an identification system.

2. Connect provenance and identity

Record the recognised identifier, received material lot, associated documents, receipt date and conditions, and acceptance decision. Preserve the connection between label and certificate: a valid document referring to another lot does not resolve the requirement.

A taxonomic name change does not necessarily mean a new strain. The EDQM FAQ dated 4 November 2024 clarifies that, for strains cited in the Ph. Eur., the culture-collection reference takes precedence over the name when taxonomy changes. Document the correspondence; do not rename materials in a way that loses the original identifiers.

Identity checks need resolution appropriate to the question. Species confirmation alone does not establish a specific documented lineage. For this limitation, see microbial identification and system reliability.

3. Build the hierarchy without inventing passages

WHO good practices, 2011, section 6.2, distinguish reference strains, reference stocks and working cultures. Define local terms, relationships and permitted operations according to the applicable method and procedures. Do not confuse lot number, container identifier and passage number.

Original document lineage: starting material and origin document → identified reference stock, where applicable → working reference and container → performed control → associated test and decision. Each link must identify the record, date, author and preceding material. This scheme represents documentary relationships, not a preparation procedure.

The definition of a passage and the permitted limit must come from the applicable source, not a universal number. In the sense of VIM 2.41, metrological traceability concerns a measurement result and its calibration chain with uncertainty contributions. Traceability of a strain's history does not establish that property by itself.

4. Govern storage and status

Link each container to its location, equipment, specified conditions, expiry or permitted use period, and authorised status. Operating conditions must come from relevant documentation and approved procedures. A known inventory position does not demonstrate that conditions were maintained.

Define access, responsibility for alarms and transfers, anomaly recording and blocked-material handling. Following an equipment failure, reconstruct which containers were present and which data are available. Do not erase history by simply replacing a code or moving the material to another unit.

5. Connect use and relevant checks

Before use, check declared identity, status, permitted period and the controls required for that function. Record which container was used, by whom, when and in which test. Suitability verification may concern identity, purity or functional response according to the method; these checks do not all answer the same question.

Organise withdrawals and records to prevent mix-ups. A digital system can flag inconsistencies only if entered identifiers and relationships match the actual material.

6. Assess deviations and associated tests

Simulated case. A working reference has a legible label and a recent passing species-identification check. The record connecting it to the preceding stock is missing. It has been used to control several media lots. Recent identification does not reconstruct the missing link.

The laboratory blocks further use, retains data and material under its procedures, and seeks verifiable contemporaneous evidence: registers, electronic associations, transfers and original documents. A statement reconstructed from memory does not become an original record. Any supplementation must show its date, author, source and reconstruction limits.

With QA, assess completed controls and the tests that depend on them. If the gap remains unresolved, state which requirement remains unproven and decide under the procedure. Replacing material may enable future work; it does not automatically close historical impact. The same principle applies to excursions or unexpected responses.

7. Assign responsibility and maintain competence

Assign responsibility for acceptance, inventory, use authorisation, review and end of use. Assess competence in recognising inconsistencies, not merely completing fields. Periodic review should look for containers without a status, missing links and untraceable tests.

Biosafety depends on the material and activity through a specific risk assessment consistent with the WHO Laboratory Biosafety Manual, fourth edition, 2020. Manage access and end of use through authorised procedures; closing inventory does not mean deleting records supporting results already issued.

Sources and consultation limits

• WHO TRS 961, Annex 2, 2011: public full text, section 6.2.
• USP 1117, 2022 record: public scope preview; verify detailed requirements in the authorised effective text.
• EDQM FAQ 2024, VIM 3 §2.41 and WHO LBM4 2020 overview, linked above: identity, terminology and biosafety framework. No operating protocol is inferred from previews alone.