Cytotoxic effect of a T-strain mycoplasma (Ureaplasma urealyticum) on cultured normal human cells (WI-38)

Normal human embryonic lung fibroblasts (WI-38) were infected with Ureaplasma urealyticum, a urea hydrolysing mycoplasma. It was possible to observe reduced rates of multiplication of infected cells and reduced plating efficiency as well as the morphological changes usually associated with mycoplasma infection of animal cells in vitro. The cytotoxic effect on multiplication was sensitive to aureomycin but not penicillin. It was not related to depletion of amino acids or nucleic acid precursors from the cell culture medium but appeared to require that the host cells be growing. Ureaplasmas could not be recovered from cell culture medium after 4 days post infection and their characteristic urease activity could not be demonstrated either in cell culture medium or associated with the cells after the first cell subcultivation. [³H]TdR was incorporated into the nuclei of infected cells and the percent labelled nuclei was reduced compared with uninfected cells. Nuclear labelling indices of infected cells increased as the cells were subcultivated by trypsinization suggesting that the ureaplasmas were removed from the host cell surface by this treatment. In general, the effects of ureaplasmas on WI-38 cells do not appear to be as pronounced as effects of other mycoplasmas on animal cells in culture. It is clear, nonetheless, that the urea hydrolysing mycoplasmas can infect cells in culture and cause discernible effects on the growth and metabolism of these cells.