Writing SOPs a tissue culture lab will actually follow

Why write it down

A procedure only works if people follow it

Most small tissue culture labs run on a method that lives in one or two people's heads. That works until the person who always makes the media is away, a new technician starts, or a run of contaminated jars needs explaining and nobody can say exactly what was done that week.

The US Environmental Protection Agency's guidance on preparing standard operating procedures (EPA QA/G-6) describes an SOP as written instructions that document a routine or repetitive activity, so it is done the same way whoever does it. The same guidance is blunt about the limits: a badly written SOP is of limited value, and the best written SOP fails if it is not followed.

It also makes a point that applies directly to media work. An SOP is still needed when you use a published method, because it should spell out the lab's own steps in more detail than the paper does, and say where the lab departs from it. A Murashige and Skoog recipe in a journal is not your lab's media day. Your SOP is.

Where to start

Write the first SOPs where one mistake reaches many vessels

You do not need a binder of forty procedures in the first month. Start with the tasks where a single slip is copied into every jar that follows.

Media preparation comes first, because one weighing error or a skipped pH check ends up in every vessel poured from that batch.

The autoclave is next: how it is loaded, which cycle is used for media and which for tools or waste, and how a run is checked and logged.

Hood work and aseptic technique cover how the cabinet is started, wiped down and loaded, how tools are sterilized between cuts, and what goes in and out of the work area.

Explant disinfection should name the disinfectant, strength, contact time and rinse your lab has settled on for each species or tissue type. Those choices vary by species and protocol; the SOP's job is to make Tuesday's treatment the same as Friday's.

Transfers and subculture cover the order of work, how vessels are labeled, and how many vessels one operator handles before stopping to clean down.

Contamination handling says how a contaminated vessel is recognized, recorded, isolated and discarded, and who is told. The FAO's draft practical guide for in vitro genebanks asks for contamination to be monitored and managed, and for contaminated and low-quality cultures to be discarded immediately; a commercial lab has the same need for a written rule.

Anatomy

What a good SOP contains

EPA QA/G-6 lists the parts a technical SOP may need, and they map neatly onto a tissue culture bench: a purpose, a scope saying what the procedure covers and where it stops, definitions, cautions, who is qualified to do the work, equipment and supplies, the procedure itself, quality control checks, and how data and records are managed.

Write the steps as actions. The EPA guidance asks for a concise, step-by-step format in the active voice and present tense, with enough detail that someone with a basic understanding but little experience of the task could carry it out unsupervised. A line such as "Adjust pH to the target and record the reading" is a step. "pH should be checked" is not.

Give each step that matters an acceptance criterion, a number or condition that tells the operator whether to carry on. IITA's published SOP for banana tissue culture media is a useful model of this. It sets the medium to pH 5.8 ± 0.1, autoclaves dispensed medium at 121°C for 15 minutes, and limits refrigerated storage of its iron-EDTA stock to a maximum of one month. Those are that program's numbers for its banana media, not a recommendation for yours; the point is that they are written down where the operator can check against them.

Say what to record. The same IITA SOP starts media day by writing the components on a media preparation checklist and checking each one off as it goes in. EPA's guidance notes that a checklist like this belongs to the SOP and should be referenced at the step where it is used, but that the checklist is not the SOP.

Finally, put a header on it. The IITA document carries an SOP number, a version number, an implementation date, a last reviewed date, an approval date and a named SOP owner, plus a short section on who is responsible for which part of the work. That header is what makes the next two sections possible.

Verify this

Test the draft on someone else

EPA QA/G-6 recommends that a draft SOP be tried by someone other than the person who wrote it before it is finalized. Hand the draft to a technician who did not write it and watch them run it once. Every question they ask, and every step they do from memory instead of from the page, is an edit.

Versions

Version every SOP, and sign people onto it

The EPA guidance recommends a numbering system for SOPs, with an ID, revision number, date and page count on every page, so anyone can tell which version they are holding and whether it is complete. It also recommends a master list of every SOP with its current version, and that outdated versions are archived so they cannot be used by mistake but can still be read when old records are reviewed.

Training is the other half. The University of Texas at San Antonio's SOP guidance for laboratories asks everyone who performs the work to read the SOP carefully and sign a training page, and asks that technicians demonstrate proficiency before working independently. Those are two different sign-offs, and both are worth keeping: one says a person has read version 3, the other says someone watched them do it correctly.

When an SOP changes, the people trained on the old version need to be signed onto the new one. Keeping the SOP version on each media batch and transfer record, alongside the operator, is the kind of per-lot record keeping lab software such as xPlant Pro is built for. Paper works too, as long as the version number is written down every time.

At the bench

Keep the current copy where the work happens

EPA QA/G-6 says current copies of SOPs need to be readily accessible in the work areas of the people actually doing the task, on paper or electronically, or they serve little purpose. UTSA's guidance suggests a binder in the lab with a section for each SOP and its training records.

In a tissue culture lab that usually means more than one copy. A short card for the hood, kept beside the cabinet rather than on the work surface. The media SOP and its checklist at the weighing bench. The autoclave SOP and run log next to the autoclave. A main binder or shared folder holds the full, signed versions.

The risk with copies is that old ones survive. When a version changes, collect and replace every posted copy at the same time, and note on the master list where each one lives. An electronic copy kept read-only, which the EPA guidance also suggests, avoids someone editing the bench copy in pencil and leaving it there.

After contamination

Review the SOP when contamination rises

The EPA guidance recommends that SOPs be updated and re-approved whenever a procedure changes, and also reviewed on a schedule, for example every 1-2 years, with the review date written on the SOP. A rise in contamination is a reason not to wait for the schedule.

Start from the records, not from memory. Which media batch, autoclave run, hood session, operator and SOP version do the affected vessels share? This is where a version number on every batch record pays for itself.

Then ask two questions. Was the SOP followed? If not, the fix may be training, or it may be that the procedure as written is not workable at the bench and people have been quietly working around it. If it was followed, the SOP itself may need to change.

Make the change, raise the version number, re-approve it, retrain and sign people onto it, and replace the posted copies. Then watch the next few batches. A revised SOP does not prove the cause was found; only what happens to the cultures afterward can tell you that, and even then contamination can have more than one cause.