Abstract
Young adult mice were inoculated intravenously with strains JB or Peter C of Mycoplasma pulmonis. A few were inoculated intranasally with strain JB. This strain but not Peter C was isolated for 50 days or more from the urines of more than half of the mice. Those of strains TO, C3H and CBA, but not CFLP, were susceptible. Recovery of mycoplasmas was intermittent and sometimes the numbers isolated varied within individual mice and between mice of a particular strain, ranging from 5 X 10(1) to greater than or equal to 5 X 10(7) colour-changing units/ml. Fifty serial passes of M. pulmonis, strain JB, in mycoplasmal medium resulted in attenuation, the organisms after inoculation of TO mice not being recovered from the urine and excretion not being stimulated by treating the mice with progesterone. At autopsy, the organisms of early passage were usually but not invariably isolated from the kidneys of mice that had been urinary excretors. About half of the latter had no renal histopathological changes. The others had usually minimal renal perivascular lymphocytic infiltrates but occasionally more widespread inflammatory changes. The findings may have relevance to the spread of mycoplasmal infection within mouse colonies and suggest that an association between such infection and nephritis in other species, including man, should be sought more closely.