Tully, Joseph G. (National Institute of Allergy and Infectious Diseases, Bethesda, Md.). Production and biological characteristics of an extracellular neurotoxin from Mycoplasma neurolyticum. J. Bacteriol. 88:381-388. 1964.-Toxigenic strains of Mycoplasma neurolyticum were found to produce a potent extracellular neurotoxin for mice under a variety of cultural conditions. The observed biological characteristics of this toxin were quite similar to those originally described by Sabin. The toxin was again found to be readily inactivated by prolonged incubation and, when separated from Mycoplasma cells by filtration, possessed a greater heat resistance than whole cells. Young mice and rats were generally susceptible to neurotoxin, whereas most other experimental animals were resistant. Filtration results confirmed a minimal reproductive unit of 125 to 200 mmu for two neurotoxic Mycoplasma strains, with both cell-free filtrates reproducing the rolling disease syndrome in mice. Twice-washed Mycoplasma cells were also observed to be as neurotoxic as filtrates. Plate counting results revealed an intravenous ld(50) of approximately 3 x 10(8) washed cells for young mice.