contamination in establishing stable cell lines - (Dec/09/2009 )

Hi,

I have a problem in establishing stable cell lines. After days of selecting for stable colonies, I picked on some of them, and now they are in 24-well dishes.

Before the wells get confluent, there is something flotting all over the wells. First I assumed that it is debris and ignored (cuz it seems exactly like debris!), but then, it starts to amplify. Believe me, despite of careful washing with PBS, these things won't dissapear and end up to get increased by size and number. Few days later I can even see them by naked eyes.

I threw them all out and started it from the scratch, but I am very depressed as it apprears again..

I attached an image of it. The stable cell of mine is in yellow circle and the one inside of the red circle is what I am talking about.

What do you think it is? Definitely I think it is something other than dead cells.

To test the medium, take some and place it into an empty well, if it grows stuff then it is contamination. To me it looks like debris from FCS.