I used a pressure canner and made agar dishes and sterilized my substrate. The agar dishes that I didn't inoculate stayed contam free, so I'm pretty certain it was the syringes. But I'm sure it depends on who prepares them. All the cleaning and sterilizing I did before actually doing the 5 minutes/day of work was what was overwhelming for me. To still get contam after that was just too demoralizing. I might try again sometime with commercially-prepared substrate/spawn.