You should be fine, anitbiotic means it kills/reduces bacteria. You will still have problems with molds and such because they will germinate just like mushie spores will. You should try and use a HEPA glove box or flow hood if you are not using H2O2 in your agar.If you have several jars of mycelium going, You can take a chunk of one (only a few strands is needed) and place on a perixide/agar plate and go from there. Just remember not to go from plate to plate to plate for ever. You need to start with fresh cultures now and then or you will have a problem with senescence (strain degeneration and loss of viability)
For the peroxide/agar info just do a search for Placebo or chestercopperpott and you will find good info.
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-ChesterCopperpott-
"Old enough to know better, young enough to do it anyway."