My 3 flasks of 293T cells have something in them that I've never seen before.
It doesn't look like bacterial contamination or like fungus. I took a picture for you to see.
There are tiny cells in between the 293T cells that look like they are colonizing the flask and forming some structures and the 293T cells are not suffering at all. On the contrary, they look like they are liking this synergy. The medium is clear and red and I don't think it's contaminated. We usually use IMDM with 10% FCS and penicillin/streptomycin and L-glutamine added in the medium.
Everyone in our lab checked the cells, even senior lab technicians with over 20 years of experience in cell culture and no one has seen this.
Do you have any idea what could it be?
Hello Marija Janevska
It appears to me like yeast contamination at the initial stages. At 100x magnification yeasts appear as separate round or ovoid particles or in chains of two to four or more particles and can sometimes be multi-branched. The appearance of chains is due to the most common form of replication called budding. Yeasts are easily distinguished from bacteria by size. Yeasts are larger than bacteria and smaller than typical mammalian cells.
Initial stages of yeast contamination are difficult to detect macroscopically, as the pH changes only slightly, initiating little or no color change in the medium containing phenol red as pH indicator.
You may visualize using phase contrast at 100x - 400x magnification. Phase contrast facilitates detection, especially at low contamination levels. Yeasts appear as ovoid bright particles between the cells. They can exist as mentioned above as single cells or in the form of chains or branches.
You may refer to the link below for more information on yeast contamination in culture.
https://unclineberger.org/tissueculture/contaminant/yeastcontam/
You may want to consider this possibility as well.
Best.
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