| When growing PF style I flame sterilize the contamination barrier after each injection with a sweeping motion. Then cover the top of the jar with foil and flame sterilize again. Be sure to use a sweeping motion with the foil or you will burn a hole in it.
I define flame sterilization as sweeping a torch (i.e. propane torch or Bunsen burner) over the lid of the jar. It causes the vermiculite to heat up and kill any contaminants that may have entered through the needle holes during the injection. The spores themselves are safe from the heat because they have trickled down the sides of the jar. Do NOT flame the sides of the jar, only the lid or else you will destroy the spores.
Simply working underneath a flame helps to create a sterile work zone when doing inoculations. It is a basic microbiology sterile technique.
PS – It is also a good idea to wipe clean and flame the needle before each injection, even if it does kill the spores that may already be in the needle tip. Better safe than sorry. |