Could easily be cell debris. Some (most) cells just sometimes push out little blebs of rubbish that float around thereafter.

Of course, it could be mycoplasma, which has a habit of looking a lot like cell debris (and which tolerates most antibiotics relatively well).

What it most likely isn't is...any other kind of bacterial or fungal infection. Most bacterial infections are rapid and dramatic (you'll be able to see millions of tiny dots whooshing around, and the media will turn visibly cloudy), and most fungal infections are either obviously yeast (you can see the actual yeast cell shapes under light microscopy) or obviously filamentous (you'll see the hyphae spreading through your culture).

You could always try a mycoplasma testing kit (it's basically PCR for mycoplasma DNA), but that is usually reserved for cell lines that you're planning to keep for the foreseeable future. For primaries, which are generally prepared fresh for each experiment, it might be a waste of resources.

My advice would be to assume it's cell debris, and just carry on with your experiments.

Obviously, keep all your primaries in a separate incubator to any long-term cell lines, because if it IS mycoplasma, you really don't want that spreading to your cell lines.

John Hildyard

Thank you so much sir.

You just made my day :)

I do keep my primaries in a separate incubator, in order to avoid any cross contamination.

Once I'll finish with the experiments I will run a mycoplasma test and clean everything.

Have a nice day ahead.

Sincerely

Kyriaki

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Hello Kyriaki Kyriakidou

I agree with John Hildyard But you should consider other possibilities as well. Many researchers have faced this type of problem. Please refer to the two articles attached for more information.

Article Got black swimming dots in your cell culture? Identification...

https://www.biorxiv.org/content/10.1101/366906v1.full

Best.