Hello all, I'm hoping someone can help me. I am culturing primary adipose-derived mesenchymal stem cells isolated from the subcutaneous and visceral adipose depots of male Wistar rats. I have attached photos of an unknown contaminant that has appeared suspended in the media of some of the plates after the initial isolation. The cells are being cultured in DMEM (DMEM 4.5 g/L glucose w/L-UltraGln w/ sodium pyruvate) + 1% penicillin-streptomycin. Please let me know if you may have an idea of what it could be.

Thank you in advance.