Use of Merocyanine 540 and Hoechst 33258 for the selective killing of contaminating mycoplasmas in cell cultures.

Mycoplasma infection can substantially affect the biological properties of cells in vitro. We have devised a method for the selective killing of mycoplasmas, e.g., A. laidlawii, M. fermentans, M. hyorhinis and M. arginini, from experimentally infected cell cultures. This approach is based on the differential binding of the lipophilic fluorescent probe Merocyanine 540 followed by illumination with visible light. The efficiency of the procedure depends on the Merocyanine 540 concentration, the intensity of illumination, and the presence of oxygen in the medium. When A. laidlawii contaminated corneal endothelial cell cultures were treated simultaneously with Merocyanine 540 and DNA-binding fluorochrome Hoechst 33258 and then illuminated, a significant degree of eradication was observed, even after one cycle of treatment. This combined treatment is therefore recommended as an effective method of purging mycoplasmas from contaminated cultures.