Mycoplasma is a prokaryote with a size of only 0.2～0.3 μm in size, it does not have cell wall and could penetrate through general filter membrane (0.22～0.45 μm). There is a high possibility of mycoplasma contamination during cell culturing. It is found in research that when cells (especially sub-culture cells) are contaminated by mycoplasma, DNA, RNA and protein expression in cells might change, however, cell growth rate is generally not significantly impacted, therefore, mycoplasma contamination is usually difficult to notice.