Effect of Animal Passage on Arthritogenic and Biological Properties of Mycoplasma arthritidis

Determinations of the ED(50) of cultures of Mycoplasma arthritidis disclosed the existence of great diversity in the arthritogenic properties of the various strains. In most cases, the ED(50) values were lowered after passaging in rats, and a more severe arthritis with a shorter period of onset was observed. Heavy suspensions of arthritogenic M. arthritidis did not appear to induce any toxic symptoms. Prior injections of endotoxin did not enhance the toxicity of M. arthritidis suspensions. The more arthritogenic strains grew more slowly in the basal medium and remained viable for longer periods of time than those with lower arthritogenic properties. All strains were identical on the basis of complement-fixation tests. Minor differences observed between strains during gel-diffusion studies could not be correlated with arthritogenic properties. Arthritogenic strains appeared to be less susceptible to the inhibiting action of rabbit antisera than were the nonarthritogenic strains.