I've ran a time series imaging experiment for CHO cells where I replenish the media and image a 24-well plate every 24 hours. These cells are under Puromycin treatment and some are induced to be resistant. In wells that have very few cells, I'm noticing small black dots that wiggle around and move near the center of the well. I have a video and some images of the objects. I'm worried that it's Achromobacter. Has anyone dealt with this issue before? Maybe during puromycin treatment?