Last Updated on February 22, 2024

Agar plates, otherwise known as petri dishes, play an integral role in microbiological research for culturing bacteria, fungi, and other microorganisms.

Though they are easy to prepare and require minimal equipment to culture, clean-up, and disposal can be messy and potentially risky. The user must safely sterilize the plate before disposal to minimize the risk of harmful microorganisms contaminating both inside and outside the laboratory environment.

That’s why we’ve prepared a detailed, step-by-step guide for the optimal methods for sterilizing plastic petri dishes and agar plates in an autoclave.

  1. Collect Used Plates
    Collect used Petri dishes/culture plates with agar. Cultured agar plates/Petri dishes should be left as-is with agar and covered to prevent the spread of microorganisms and reduce the risk of contamination.
  2. Load Agar Plates/Petri Dishes
    Load used culture plates in the plastic petri dish/agar plate sterilization basket. Remove covers and place them aside before loading the agar-filled portion into the specialized perforated basket. Place dish/plate covers on the agar-filled portions at the end.
  3. Set Up Bucket and Stand
    Set up the stand inside the specialized solid bucket and fill it with water to prevent melted media from solidifying inside the bucket. The stand will place the specialized perforated basket on the water, allowing the melted media to fall through. Fill the water to about half of the height of the stand.
  4. Load Bucket with Stand
    Place the water-filled bucket inside the autoclave. Next, place the perforated basket with disassembled plastic Petri dishes/agar plates, resting the basket on the stand.
  5. Run Cycle
    Close the autoclave and run a normal sterilization cycle for at least 20 minutes. Please note that the sterilization time differs with the number of plastic Petri dishes/agar plates.
  6. Unload
    Remove the perforated basket after the sterilization cycle is complete and the autoclave temperature has cooled down to a safe level. Even though the temperature is registered at a safe level, please be mindful of hot steam, liquids, and media.
  7. The Chunk
    Note that the plastic Petri dishes/culture plates and lids have melted and re-forged into a sizeable chunk. Some of the agar material has been trapped/fused into the plastic, and though it should be sterile, avoid touching parts where agar is exposed to prevent a mess. Most of the agar has melted and mixed with the water inside the bucket.
  8. Throw Away- No Mess!
    Dispose of the plastic chunk and pour water into a biohazardous liquid receptacle or a drain where it can be safely disposed of and eventually processed. Safe, easy, and no mess!

Do You Have to Use an Autoclave?

You may have heard about alternative plastic petri dish sterilization methods that don’t require autoclave sterilizers, such as microwave ovens or caustic chemicals. While these methods may kill a significant portion of bacteria, they won’t kill all of them because of the resistance of certain microorganisms.

To truly sterilize Petri dishes, you must use an autoclave, as only high heat, moisture, and pressure can effectively kill the full range of microorganisms, which can persist even under unusually harsh conditions.

Biohazard/Bio-Waste Bags: Yes or No?

Another standard method for disposing of plastic Petri dishes is to place them in bio-waste/biohazardous waste bags and sterilize them in autoclaves.

While this method does achieve sterilization, it has some significant downsides, as liquified agar mixed with biomaterial can easily leak and cause a mess within the laboratory or on the way to waste disposal areas.

When paired with the correct autoclaving accessories, the autoclave sterilization method above deactivates harmful microorganisms while creating the least clean-up.

Autoclaving Plastic

Most plastic petri dishes are made of Polystyrene, which will melt if you bring it above 50 degrees. You may read places that you can’t autoclave certain kinds of plastic, and that’s true if you want to reuse Petri dishes. However, it’s perfectly acceptable to autoclave them for disposal.

If you want more sustainable or reusable options, try glass petri dishes and follow the specific instructions provided.

Autoclaving Plastic Petri Dishes Can Be Simple

Properly sterilizing plastic Petri dishes and agar plates in an autoclave is critical in ensuring laboratory safety and environmental protection. By following the detailed steps outlined in this guide, users can effectively deactivate harmful microorganisms, minimize the risk of contamination, and ensure a clean, safe disposal process. While alternative methods like microwave ovens or chemical treatments may seem appealing, they fail to achieve complete sterilization. Autoclaving, with its combination of high heat, moisture, and pressure, remains the most reliable method. Sterilizing Petri dishes in an autoclave is not only straightforward but also essential for maintaining the highest standards of laboratory hygiene and bio-safety.

If you’re looking for the right autoclave for your lab or business, look no further. Our autoclaves are high-quality and efficient. Check out our products or contact us today!

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