As far as I know, we have some symbiotic bacteria for OSCC cell line. The bacterial species that contaminate the OSCC are usually non-pathogen Staphylococcus strains. However, seeing the particle moving in your culture does not prove the bacterial contamination and you need to confirm that by the microbiology test if you are interested. Have you ever done Mycoplasma test on your cell?
throw it, if you have contamination, even if it grow, your results will be biased, if this is cell death, it is the same, furthermore, you take the risk to contaminate the lab.