--- I had this problem before, I made new medium, and it went away. This time I made new medium, and it did not help. So, I made another batch of medium and filter-sterilized it (0.2 um) after adding serum (usually I filter and then add serum). This also did not help.
-> This would seem to rule out fungi or most bacteria, leaving mycoplasma and viruses as possible contaminants. However, I cannot figure out how they might be getting into the culture.
--- I have autoclaved the incubator racks and sprayed the incubator interior with 70% ethanol.
--- I have started several cultures from frozen stocks with new medium. I have used stocks from different batches that have produced good cultures in the past.
The problem persists, if it is a problem. While this is not how my cultures usually look, I was wondering if anyone knew if it was normal for this to periodically happen in these cell lines.
Any ideas, suggestions, etc. are greatly appreciated.
A couple of pics...