TOMY-Autoclave-screenIn a lab, a lot is riding on the assumption that your autoclave is sterilizing as intended. Any contamination can derail tests, alter results, and compromise the safety of your lab. And while autoclaves are easy to operate and maintain, it can be difficult to ensure that an autoclave does what it says without using specific tests.

That’s why the CDC recommends monitoring your sterilization procedures using a combination of biological, mechanical, and chemical indicators. However, spore testing your autoclave is the most effective biological method for ensuring sterilization.

What Is Spore Testing?

Spore testing, also known as biological monitoring, involves subjecting highly resistant microorganisms (most commonly Geobacillus stearothermophilus) to sterilization to assess whether or not your autoclave is functioning correctly.

Since spores are the most resistant to sterilization, and common disinfectants are ineffective against them, spore testing acts as a stress test for your autoclave. If it can kill the spores, it can kill nearly anything.

Why Do You Need To Spore Test?

For daily usage and monitoring, labs generally use mechanical and chemical indicators. These can include

  • Pressure gauges
  • Temperature charts
  • Indicator tapes
  • And printers and data loggers

Chemical indicators are divided into single-parameter and multi-parameter and provide information about one or several factors, including time, temperature, and the presence of steam. They verify that the autoclave is reaching temperature and pressure.

Most of these are good practices to maintain and provide a daily check-in on the autoclave, so labs shouldn’t eliminate all of them.

However, while these processes can quickly identify mechanical failures or procedural errors, they’re not the most accurate way to see if the autoclave works as intended. As mentioned above, spores can be incredibly hardy, making them difficult to eradicate.

Should I still use chemical and mechanical indicators?

El CDC recommends using chemical and mechanical means but stresses that they don’t verify sterility. So, even if all the mechanical and chemical indicators say that your autoclave is sterilizing, it’s not guaranteed.

The best way to assess whether your autoclave is functioning as intended is to push it to its limits and put it up against what it’s actually combating. That’s where spore testing comes in. Spore testing makes sure that even when subjected to the most demanding test, your autoclave is eradicating all possible contaminants.

How Often Should I Spore Test?

According to the CDC, you should spore test at least once a week. This frequency should be enough for most operations unless your lab is exceptionally high volume or frequently sterilizes hazardous objects.

It also depends on the regulatory standards your industry is subject to. For example, the American Dental Association recommends weekly spore tests, but hospitals and research labs may follow different regulatory organizations. Make sure to research the specific spore test requirements for your industry.

How To Spore Test Your Autoclave: Step-by-Step

Spore testing is not a particularly intensive process overall, but you need to take care to perform the steps to ensure the tests aren’t compromised.

Step 1: Obtain spore test kits

There are two principal types of spore tests, which are also known as biological indicators (BIs):

  1. In-office spore tests that use an incubator: In-office spore tests provide a faster turnaround time, usually within 10 hours. They are also generally simple to perform.
  2. Third-party laboratory testing: Laboratory testing requires you to mail in your test kit, which means the turnaround time will be at least a few days longer.

Both tests involve potential error, though laboratory testing may provide more precise results. However, for busy labs requiring weekly tests, it’s generally preferable to perform in-office tests. You can always combine the approaches and perform them both on a rotating basis.

Whichever type of test processing you choose, always verify that the test kit isn’t expired. They generally have a long shelf life (around two years), but an expired test will be ineffective, and you’ll have to repeat the process.

Step 2: Load and run the autoclave

Your load should be representative of a typical cycle, so do not under or overfill the autoclave, as this could affect results. Place the test in the most densely packed area, preferably toward the center, since that’s the most difficult area to sterilize.

Also at this point, take an identical test and leave it outside of the autoclave to use as a control for the operation. You want to ensure the spores are viable; using a control is the easiest way to guarantee that.

Once loaded, run a standard cycle. The goal is to mimic normal operations most closely.

Step 3: Incubate the BI or send it for testing

If you’ve chosen an in-office kit, remove the BI and follow the test’s specific instructions for incubation, including instructions for temperature and length of time.

If you’ve chosen a send-away test, send it promptly. Otherwise, results may be compromised.

What Do the Results of a Spore Test Mean?

Once you’ve completed the spore test, all that’s left is to interpret the test.

Consult your specific test’s manual for instructions on how to proceed for in-office tests. In general, the test involves looking at the BI for a color change. Just make sure to compare it to the control test to ensure your assessment is correct.

There are three possibilities:

  1. Successfully sterilized: There is no color change from when you put it in the autoclave, and it’s a different color from the control—this is a negative test or a successful run. You can assume the last batch that you autoclaved has been successfully sterilized.
  2. Test failure: It’s changed color, and so has the control. This means your test was positive and is a failed result. Do not assume the last load was sterilized if this is the case. You need to check every step of the autoclave process for operator error and mechanical failure and rerun the test.
  3. Inconclusive: If the control BI hasn’t changed color, you may be dealing with dead spores, so rerun the test with a different kit until the control shows growth.

For third-party testing, all you need to do is wait until they send the results, which will depend on the lab.

Whichever method you use, if you have a failed test, you should immediately retire the autoclave from active service until the problem is dealt with.

It may be an operator error. You should reassess how you load the autoclave, double-check the autoclave’s parameters, and ensure that you’ve packaged everything correctly. The other option is a mechanical failure, so check common culprits like the gaskets. If the tests repeatedly fail, it’s time to contact your manufacturer.

Make Sure You Spore Test Your Autoclave

Autoclaves are labor-saving devices that keep your lab running smoothly and safely. But relying on your autoclave’s function alone is not enough. Spore tests allow you to verify that your articles are actually sterilized.

If you want to purchase an efficient, simple-to-run, and space-efficient autoclave, TOMY has what you want. Check out our autoclave selection and contact us to learn more.

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