Percoll centrifugation eliminates mold contaminants from cell cultures

Enrichment and Recovery of Mammalian Cells from Contaminated Cultures Using Aqueous Two-Phase Systems

This Article describes a density-based method for removing contaminants, including microorganisms and nonviable cells, from mammalian cell cultures using an aqueous two-phase system (ATPS). The properties of a 7% w/w polyethylene glycol (PEG)-11% w/w Ficoll ATPS can be tuned to prepare a biocompatible system that removes contaminants with little to no adverse effects on the viability or growth of the cultured cells after treatment. This system can be used to enrich cell culture populations for viable cells and to reduce the number of microorganism contaminants in a culture, which increases the chances of subsequent antibiotic treatments being successful. We test the effectiveness of our method in model contaminated cultures of both adherent (HeLa) and suspension (HL-60 II) mammalian cells contaminated with bacteria (E. coli) and yeast (S. cerevisiae). An average of 70.2 ± 4.6% of HeLa cells added to the system are subsequently recovered, and 55.9 ± 2.1% of HL-60 II cells are recovered. After sedimenting to the interface of the ATPS, these cells have an average viability of 98.0 ± 0.2% and 95.3 ± 2.2%, respectively. By removing unwanted cells, desired cell populations can be recovered, and cultures that would otherwise need to be discarded can continue to be used.

Fractionation of cells and subcellular particles with Percoll

At present, centrifugation is the most common method for separation and isolation of cells and subcellular particles. The technique can be used for a wide range of applications. During latter years it has become obvious what a powerful method density gradient centrifugation is, especially when used in conjunction with sensitive assays or clinical treatments. The most active areas for use of density gradient centrifugation include purification for in vitro fertilization of sperm of both human and bovine origin, isolation of cells for cell therapy of patients receiving chemo- and radiation therapy and basic research both on cellular and subcellular levels. These treatments and investigations require homogeneous populations of cells and cell organelles, which are undamaged after the separation procedure. Percoll, once introduced to reduce convection during centrifugation, has proved to be the density gradient medium of choice since it fulfills almost all criteria of an ideal density gradient medium. Recently good results have also been obtained after silanization of colloidal silica particles, e.g. BactXtractor. The latter medium has proved to be useful in recovery of microorganisms from food samples free of inhibitors to the Polymer Chain Reaction (PCR). The separation procedures described for Percoll in this review seem to be applicable to any cells or organelles in suspension for which differences in size or bouyant density exist. Furthermore, since Percoll media are inert, they are well suited for the separation of fragile elements like enveloped viruses.