Comparison of methods for detection of Mycoplasma pulmonis in experimentally and naturally infected rats.

Isolation, indirect immunofluorescence, an enzyme-linked immunosorbent assay (ELISA), and histopathological examination of tissues for characteristic lesions were evaluated for their efficiency in detecting Mycoplasma pulmonis infection in rats. Whereas all of the methods were efficient in naturally infected Sprague-Dawley rats, none of the methods consistently detected infection in F344 rats experimentally infected with low doses of the organism. In the experimental infections, however, the success rate of any method was directly related (P less than 0.05) to increasing inoculum dose and time postinoculation. Collectively, the data indicated that isolation of M. pulmonis was the most efficient single detection method and the nasopharyngeal duct was the best single site to culture, although sampling of multiple sites within the respiratory tract increased the rate of isolating the organism. The ELISA was understandably the least sensitive method in the low-dose, experimentally infected rats because of the time required for development of a detectable serum antibody response. Although each of the four methods identified a high percentage of naturally infected rats, the ELISA was the most efficient method in these animals as it was uniformly positive. The use of combinations of methods was found to increase the rate of detection of M. pulmonis infection in both experimentally and naturally infected rats.