Contamination of cell cultures with Mycoplasma species can affect your cells in numerous ways, most of which will reduce the reliability, reproducibility, and consistency of your experimental results. The type and severity of these effects will often depend on the cell type you are using. Some of the general effects observed in eukaryotic cells can include:
Contamination with certain Mycoplasma species can also cause cytopathic effects, characterized by stunted, abnormal growth and degenerated cells, likely due to the promotion or inhibition of apoptosis1. This is a major problem for research, as well as during the manufacturing and processing of biological products and biopharmaceuticals because contamination can result in reduced yields or loss of an entire product batch. In addition, hybridoma cells, typically generated to support applications like antibody manufacturing, can show characteristic effects when contaminated with Mycoplasma, such as inhibition of cell fusion and a lower yield of monoclonal antibodies2.
References:
1) Rottem et al. (2012). Book chapter 3, book: Biomedical Tissue Culture, ISBN 978–953–51–0788–0
2) Drexler HG, Uphof CC (2002). Cytotechnology 39: 75–90