Mycoplasmas as pathogens.

This paper concerns several animal models for study of pathogenic mechanisms in mycoplasma infection. Although these will seem remote from the general topic of this symposium, it is conceivable that some of the mechanisms may have implications for chronic pulmonary disease. Mycoplasmas are known to be causative agents in acute and chronic pulmonary infections in several species of domestic animals. One species, M. pneumoniae, is now established as the cause of primary atypical pneumonia in man, and the way may now be open for investigation of the role of mycoplasmas in other varieties of lung disease. Toxicity of mycoplasmas There are now known to be four unrelated species of mycoplasma that cause death by virtue of a toxic property of the living organisms, in a manner reminiscent of the toxicity of certain viruses. The first two of these, which cause toxic symptoms and death in a generally similar manner, are M. arthritidis, the causative agent of acute and chronic arthritis in rats and mice, and M. pulmonis, a presumed cause of acute and chronic lung disease in rodents.' When cultures or washed suspensions of live organisms of either species are inoculated by vein, the animals become prostrated, usually after a latent interval of three to four hours. They usually die within a period of 12 hours or less; with very large doses (101-1011 organisms), death can be brought about within as short a time as one hour after inoculation. The organisms are required to be alive for this to work. Animals can be partially protected by pretreatment with tetracycline or gold thiomalate, suggesting that the organisms may be elaborating a toxic material after being injected. Extracts of sonically disintegrated mycoplasmas are without toxicity, nor can any exotoxin be demonstrated in culture filtrates. The toxicity of these two strains has a high degree of species specificity; the only laboratory animals thus far shown to be affected by either M.