is it a contamination or harmless debris - (Oct/22/2012 )

Dear Guys,
I am culturing HePG2 and yesterday I was in a hurry, I know it is not good to work in this condition, but this what I had to do.
After 18 hrs of culturing my cells, I can see something under microscope, I suspect infection.
and I want to do some experiment, and I can't risk if it is infection.
or it is harmless debris from my FBS in medium
No change in medium pH or turbidty, just tiny things swimming in my medium.
These things are not really spread, u can find them in certain places only, while rest of plate has a less amount.
these are 20X photo of my 3 plates for ur opinion.

what I think I would do, I have 3 plates, I can use one for my experiment, then leave other 2 for one or two more days and see if these things become worsen, like pH change, turbidity, fully occupied the plate.

please give me ur opinion

Thanks in advance

If you are talking about the dark lumps of stuff between the cells, then it is very likely to be debris from dead cells, it is a bit big for bacteria and too irregular to be most cell types, unless they are a clustering form (e.g. staphylococci). However, the fine stuff you posted in the last image could well be contamination.

It would be unusual to note contamination after 18 hours, that is pretty quick, but there are plenty of species that could grow that fast. The most common contaminations are from E. coli, and a few skin bacteria, many of them are motile too, so you can often see them swimming about.

after 48 hrs, no change at all (No pH, or color or increased growth of these intruders).
So I believe it was harmless debris.
Thanks for advice

bob1

Maybe they are yeast.
Have you cooked Bread with yeast in your home?