How to Make Agar Plates
Used for fingertip testing and sterility assurance. You should use Tryptic Soy Agar (TSA)1 as your growth medium. If you have the ability and means to use Fluid Thioglycolate Medium (FTM) then you should use it in addition to TSA for your sterility testing.2 USP 71 says that both TSA and FTM need to be used for sterilization tests, however, FTM is expensive and difficult to procure and so we have opted to leave it out of this guide.
Your TSA plates for fingertip testing and for sterility testing need to be prepared slightly differently. Make TSA with neutralizers for fingertip testing.1 Make without neutralizers for sterility assurance tests. Neutralizers polysorbate 80 and lecithin are used in combination with the TSA to “to neutralize the effects of disinfecting agents”3
We’re not 100% certain what the neutralizers accomplish, but it seems like they protect the agar from any IPA residue left on gloves from cleaning.
Making Tryptic Soy Agar (TSA) plates is straightforward assuming you have the right equipment. Use the link above for an example of ratios to use when making TSA with neutralizers. Start with sterile plates, either you purchased them sterile off the internet (Amazon has them) or you sterilized them yourself in your autoclave.
Next, you should mix the TSA powder with distilled water according to the TSA package and then autoclave the now-mixed TSA in a media bottle.
When the agar cools to handling temperature but is still liquid, pour the sterile TSA into the sterile plates under a laminar flow hood or still air box. Seal with tape. Let set.