Immunoprophylaxis of experimental Mycoplasma pneumoniae disease: effect of aerosol particle size and site of deposition of M. pneumoniae on the pattern of respiratory infection, disease, and immunity in hamsters.

The distribution of Mycoplasma pneumoniae infection in the respiratory tract and the extent of pulmonary pathology were determined by the site of deposition and the number of organisms administered to hamsters. Infection of the upper and lower areas of the respiratory tract occurred when organisms were introduced into both areas by small-particle aerosol (2.3 micrometer) or by intranasal (i.n.) instillation of a 200-microliter inoculum. In contrast, when organisms were delivered primarily to the upper respiratory tract by large-particle aerosol (8 micrometer) or by i.n. instillation of a small volume of inoculum (2 or 20 microliter), infection remained limited to this area in most or all instances. When the lungs became infected after i.n. administration of a 200-microliter inoculum, the most extensive pulmonary lesions were seen in the animals given the largest number of organisms. Each of the modes of administration of M. pneumoniae initiated an infection which conferred measurable resistance to a subsequent challenge capable of inducing extensive pulmonary disease. The most effective resistance was induced by the two modes of administration which produced an infection involving the entire respiratory tract, i.e., small-particle aerosol or i.n. instillation of a 200-microliter inoculum.