How to Spore-Test an Autoclave

Updated April 17, 2017

Autoclaving is a routine, effective method for sterilising medical instruments, biological media and vaccines. However, autoclaves can malfunction or perform suboptimally for a multitude of reasons, resulting in incomplete sterilisation. Therefore, it's necessary to test autoclaves regularly with Geobacillus stearothermophilus, which is one of the most heat-tolerant species of bacteria. If sterilisation in an autoclave does not destroy the Geobacillus spores, the device is not working properly.

Read the directions on the specific spore test product you're using. Some products require you to take certain steps before autoclaving.

Place the spore test into the autoclave and sterilise for one hour, at standard sterilisation temperature and pressure.

Wait for the autoclave to depressurise and cool down, and then remove the spore test.

Spread the autoclaved spore test onto an agar plate, and place it into an incubator for 3 to 48 hours (or follow the manufacturer's instructions). If you don't have an incubator, buy a spore test that you can ship to the manufacturer for incubation.

Check the agar plates for bacterial growth within the incubation time frame specified by the spore test manufacturer, or wait for results from the manufacturing company.


You must sterilise the spore test under normal autoclave conditions. Therefore, you should include any tools and media that you normally sterilise in the autoclave. If you will incubate the sample on site, be sure to swab the spore test fluid onto the agar plate in a sterile environment (e.g., a laminar flow hood).


The spore test contains bacteria that may pose a health hazard. Dispose of the test properly through sterilisation or incineration. Do not continue to use an autoclave if it fails the spore test.

Things You'll Need

  • Autoclave
  • Spore test
  • Incubator
  • Agar plates
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About the Author

Samuel Sohlden began his freelance writing career in 2007. His work appears on various websites, with articles focusing on science and health. In 2010 he attended the Intel International Science and Engineering Fair in San Jose, Calif. Sohlden is pursuing a Bachelor of Science in microbiology from the University of Cincinnati.