Agar contamination — green mold, is this trichoderma?
38 replies · Cultivation
Working on first agar plates and getting green contamination on about 30% of plates poured. The contamination appears within 48 hours of pouring, before I've even done any transfers. Green, powdery, spreads fast. I'm assuming trichoderma but wanted to confirm and figure out what's going wrong with my pour technique.
Setup: still air box, 70% isopropyl sprayed before work, flame sterilised scalpel, agar poured while still hot (~55°C). Plates left to cool in SAB with lid cracked 1cm.
Classic trichoderma — the 'cracked lid during cooling' is your problem. Even in a still air box, a partially open plate is an invitation. Pour and seal immediately with parafilm or Micropore tape. Don't let them cool open. Trichoderma spores are everywhere and they are fast.
Also, 55°C is too hot for pouring — you should let agar cool in the flask to 50°C (hot to touch but not burning). Too-hot agar creates convection currents that pull in outside air. And make sure you're letting your SAB settle for 10+ minutes with IPA spray before touching anything.
Trichoderma confirmed. If you're still seeing 30% contamination after fixing the lid issue, suspect your agar recipe or pressure cook time. I do 90 minutes at 15 PSI minimum for agar — shorter times leave viable trichoderma spores.
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