Repeated cell culture contamination
Hi everyone, I'm fairly new in the lab life, I started 8 months ago as an intern. I'd like to ask you for a piece of advice, because three weeks ago my cell cultures, along with the ones of the PhD student who is teaching me and of another intern started being contaminated and growing mold. We suspect everything started from a dish brought in our incubator from another, malfunctioning incubator. Since then we tried everything we could: we threw away every dish, made new media, PBS and trypsin, made new backups from other PhD students, we did not share cells, media or anything anymore, we also use different cell lines (I am using FaDu and the others are primarily using Cal-27), but contamination keeps occurring between us three. Another strange thing is that others in the lab do not have this issue, even people who share the same shelf of the incubator (they use the same shelf but a different area from us three) so it's unlikely this is due to a reagent for common use or due to a general malfunctioning of the incubator. Something else we noticed is that the contamination seems to occur only in dishes, and it didn't seem to appear in flasks or 12/24-well plates. Do you have any idea about what might cause this? And also if you have any pointer about how to improve in recognizing early signs of contamination I'd really appreciate that, I don't know if there are valid guides out there maybe with pictures and stuff like that? Thank you very much, it's been weeks and this delay in my experiments is really worrying me.
Edit: I thank you all for all the advice and suggestions, I didn't expect so many of them and I'm really grateful for your contribution!