Can one use 'old' petri dishes for a microbiology practical?

Discussion in 'Supporting Biology' started by Jimbob1988, Dec 6, 2019.

  1. Morning all,

    According to CLEAPSS (GL277) it recommends using new petri dishes for microbiology practicals, and it also states using an autoclave will melt such dishes, so can one then assume there is no suitable method to sterilise old' petri dishes for this practical?

    Many thanks :)
  2. Not for plastic ones - at least not available to schools. If you have a class set of glass ones you could.
  3. Only if you use glass ones I suppose but for safety it's better to use new plastic ones and just destroy them along with any contaminated agar when they are finished with.
  4. You can sterilise them with UV as they are done in the factory but im not sure if there are any kits of the apparatus that would be small/cheap enough for school use.

    It would be very handy though because I hate having to open up a full pack of 20 or 30 to get a handful of plates out of it because then it renders the rest of the back unsterile.
  5. I re-seal my sterile packs immediately after removing the few that I need. In theory they have lost their sterility but in practice I find they are perfectly fine and grow nothing unless they are inoculated and give what is expected when they are!
    Jaytee, lizfalk, Beaker and 3 others like this.
  6. I do the same as Lesley with no problems, just seal well. I use these to start next time
  7. Plastic will melt in an autoclave
  8. mostly they are not sterile anyway, just made in a clean room.
    Lesley Newcombe likes this.
  9. If you want sterile they usually don't say so or not - have to check product information carefully to get ones which are sterile.
    I got a 500 box of these last year - not shown as sterile - but have done over 100 plates and not one was contaminated
  10. I buy them from Philip Harris which advertise them as sterile! And they seem pretty reasonable,-disposable-90-x-15mm-pack-of-500/b8h64826
  11. The sterile ones are usually irradiated.:)
  12. So how we sterilise the used petri dishes before disposing them?
  13. Resolved my friend :)
  14. autoclave at 121C for 35 minutes, is how i was taught.
    ClaireS likes this.
  15. Agar plates -
    Sterilise in an open autoclave bag (as @Paul says)
    Put in one bag and tie, then into another bag and tie.the cooled waste & place in the outside general waste bin
    JHRoss likes this.
  16. Ok but what if they melt in the autoclave?
  17. That's why you do it in an autoclave bag which keeps it all intact - the bag doesn't melt
  18. The simple answer to this question is don't use used Petri Dishes.:);)
  19. But the plates may!:D
  20. 15 minutes Paul or the sugars present may be extensively caramelised:rolleyes:
    Last edited: Feb 13, 2020
    AllantheTech likes this.