Pretreatment of animals with tetracycline protects completely against the toxic effects of washed suspensions of mycoplasmas, while tetracycline affords no protection against the exotoxin. Freeze-thawing disruption of mycoplasma suspensions eliminates their neurotoxicity, while the same treatment does not affect exotoxin. The toxicity of intact organisms is not affected by exposure to the sedimentable component of brain, nor to ganglioside. These observations are interpreted to indicate that the neurotoxicity of living mycoplasmas must be due to their production of toxin after they have been injected into the animal.

Resting mycoplasmas, suspended in Ringer's solution in dialysis sacs submerged in PPLO broth) produce considerable amounts of toxin within 15 min of incubation at 37°C. Toxin is also produced, although in somewhat less amount, by washed organisms suspended in phosphate buffer containing glucose. The formation of toxin is prevented by the presence of puromycin, but not by the aminonucleoside analogue of puromycin, indicating that active protein synthesis is involved in the elaboration of toxin.

The similarities between the neurotoxicity of the intact organisms of M. neurolyticum and Mycoplasma gallisepticum are discussed.