I have had some spots in my CHSE-214 cell culture for some time, I do not know if it is a contamination or just cell debris, the medium is not cloudy nor does it show any color change. The cells have not presented any problems in their growth.

I have changed the medium, the fetal bovine serum and even the trypsin but the spots persist. When I leave the cells without subculturing, these spots increase.

I took some of the medium from the cells and filtered it and left the filter growing on LB agar medium, but still no bacterial growth.

I did PCR against mycoplasma but it was negative so I don't know what it could be.