No abstract

The in vitro response of mouse thymocytes to various mycoplasmas was evaluated. Cultures of thymus cells from BALB mice were prepared in Earle minimal essential medium with 10% fetal calf serum. After an initial drop in viability, cell populations stabilized at approximately 105 viable cells/ml for 3 to 5 days. Concentrations of 106 to 108 colony-forming units of toxic isolates of Mycoplasma fermentans per ml killed over 50% of these cells in a dose-dependent fashion. Four other mycoplasmas (M. pneumoniae, M. hominis, M. arthritidis, and a nontoxic strain of M. fermentans) did not induce cytotoxicity of mouse thymocytes. Toxic isolates of M. fermentans multiplied in the presence of thymus cells as they were being inactivated. However, nonviable membrane preparations of these mycoplasmas were also toxic, indicating that growth of the organisms is not a prerequisite for the toxic effect. The relevance of these findings for the isolation and identification of the membrane-associated toxic factor is discussed.

A new medium, which contained a chemically defined tissue culture base ("medium 199"), was developed for the cultivation of mycoplasmas. When supplemented with albumin, glucose, serum, and yeast extract, the new medium adequately supported the growth of Mycoplasma and Acholeplasma species.