Sometimes, dead cells are round and dark in colour & look like bacterial contamination. If they are moving and not stationary that means it is a bacterial contamination. Bacterial contamination progresses very fast so after 24 hours there will millions of bactria sqiggling around! Maybe you need to add some antibiotict to the cell culture media.

Agree with Natasha, they look like dead cells. MCF-7 is a monolayer and those are round cells, that move in suspension. Possibly it may be overgrowth or bad quality of FBS or non satisfactory conditions of freezing or else...

Hi Bikash, I agree with Natasha. It could be debris from dead cells and not contamination. Are there other signs of infection like acidified yellow medium, or cloudy cultures? If it was bacterial or fungal, you'd see millions of cells in your culture.

It might be a contamination.The black dots would be cellular debris reflecting very bad cell maitenance conditions. 

Hope it can help.

Hamadi.

Bikash,

First of all you could have kept better images with MCF-7 having its complete morphology. Those black dots may be because,

1) More tripsinization of cells

2)Splitting cells when they are more confluent

3)Repeated/ vigorous pipetting

Above all are cell debris

4)Because of contamination(If it is,

(a)increasing number of blackspots than MCF-7,(b)changing of media colour quicker than regualr time, (c)moving of particles atleast 2-5mm distance i.e.,motile bacteria, (d)recurrence even after repeated PBS washes, and media changes (not after tripsinization) etc.,)

Think and trouble shoot them accordingly, reconsider about media, flasks, tips, and sterile conditions (or) use antibiotics suitable. I suggest you to take new cells from other source not form your lab .

Thank you all for comments. First of all im sorry i put the images after some time of passaging so cells werent attached well. Regarding the black dots initially i thought cell debris and i have been centrifuging and harvesting the cells cery carefully but couldnt get rid of them. I observed the dots carefully and i found them moving. Im not sure they are bacteria because cells did grow well enough and didnt find apparent color change of media. Actialky i even thawed new cells and still found same problem. Im not sure how to disinfect the lab. Is there a protocol?

Hi  I work with MCF-7 cells. 

Those cells do not look happy at all, that is not the morphology that they should have. I suggest to use less trypsine, to see an improvement in the growth and morphology. If you over trypsinized the cells you could kill them which cause cell debris. Then, what kind of movement? do they swim from one point to another? or do they stay more or less in the same point but doing circular movements? if it is the first one it is a contamination but there should be more thing to indicate it like changes in the pH or color of the media, and turbidity. If it is the second option is not a contamination, it would be just cells debris of dead cells if cells are dying because of stress conditions that could also explain the slow growth and that weird morphology.

You could also stain with  trypan blue to double check for an infection and do a mycoplasma test  

I hope it is not contamination

Good luck  

working on the MCF-7 cell line and facing a lot of problems of contamination. I can see growth. unable to solve it. we are using 4x antibiotics can we increase a dose. It is in good condition for two weeks and then gets contaminated.