SCE induction and harlequin staining in mycoplasma-contaminated Chinese hamster cells.

Chinese hamster V79 and CHO cells infected with Mycoplasma hyorhinis show elevated sister-chromatid exchange (SCE) levels but normal cell proliferation and levels of chromosomal aberrations when compared with uninfected cells. Harlequin staining patterns differ from those seen with uninfected cells at similar levels of bromodeoxyuridine (BrdUrd), indicating that BrdUrd is rapidly depleted from the medium by the mycoplasmal uridine phosphorylase and therefore becomes unavailable over the two cell cycles necessary for harlequin staining. Continuous treatment with the antibiotic minocycline restores the SCE level and harlequin staining to that seen in uncontaminated cells. The results suggest that mycoplasma infection should be suspected if harlequin staining patterns indicate a sudden decrease in incorporation of BrdUrd in cells grown in normal levels of BrdUrd.