Independence of Leukemoid Potential and Toxigenicity of Mycoplasma fermentans

The ability of cells and membranes of Mycoplasma fermentans, strain K10, to induce lethal toxicity and leukemoid disease in mice was evaluated. Lethal toxicity could be induced by viable cells (cumulative doses of ⩾ 1010 colony-forming units) or membranes (cumulative doses of ⩾ 5 mg of protein) of M. fermentans K10. However, cells and membranes, administered at sublethal doses in the protocol originally shown to result in leukemoid disease, did not induce the anticipated hematologic or gross pathological alterations. Injections of 108 colony-forming units per mouse on five successive days induced only a minimal leukocytic response (< 60% rise) six to 20 weeks after injection. Similarly, native mycoplasma membranes and reaggregated membranes administered in equivalent sublethal doses induced only negligible changes in total leukocytes, differential count, and spleen weight. The suspending media, the substrain of mouse, and the time of bleeding were not critical factors. Thus, cells and cell fractions of the K10 strain were devoid of leukemoid potential but retained the ability to induce lethal toxicity.