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Abstract
Murine respiratory mycoplasmosis (MRM), caused by Mycoplasma pulmonis, is a major complication of research using rats and mice and also provides excellent animal models for the study of a naturally occurring respiratory disease induced by an infectious agent. MRM is one of the best defined mycoplasmal diseases and is well suited to experimentation because it can be studied easily in the natural hosts (rats and mice). Furthermore, several variables affecting the pathogenesis of the disease have been identified and are easily manipulated experimentally. Although much is known about the host response in MRM, the virulence factors of mycoplasmas have been poorly elucidated.
In the studies reported here, the mouse model of acute MRM was used to screen 18 strains of M. pulmonis for their ability to establish respiratory infections and produce gross lung lesions in C3H/HeN mice. All experiments were designed to minimize host, environmental, and microbial differences to ensure that experimental results would reflect differences in mycoplasmal virulence. In addition, the same frozen stocks of M. pulmonis were used for all experiments in order to eliminate variability of the organisms over the long time period necessary for these experiments. Based on the results of these experiments, 5 mycoplasmal strains were chosen for evaluation of lung lesions in C3H/HeN and C57BL/6N mice on the supposition that virulent or avirulent mycoplasmal strains would cause qualitatively similar lesions in both mouse hosts. Next, these same 5 strains were examined in respiratory clearance experiments to identify differences among the strains in susceptibility to host nonspecific defense mechanisms. All 18 strains were compared for differences in hemolysis of red blood cells, hemadsorption, and colonial morphology and for differences in lymphocyte transformation assays. Two dimensional polyacrylamide gel electrophoresis of all 18 strains and two dimensional immunoblots were used to identify the primary regions of protein variability in M. pulmonis. Upon close examination of two dimensional polyacrylamide gel and nonequilibrium pH gradient electrophoretograms of the 5 strains used for the respiratory clearance and lesion studies, areas of protein variability were located and specific proteins were identified that may be associated with virulence.
