Susceptibility of Balb/c, C57/B6 and C57/B10 mice to infection with Mycobacterium paratuberculosis

Balb/C, C57/B10 and G57/B6 mice were examined for their susceptibility to disseminated Mycobacterium parahtherculosis infection after intraperitoneal inoculation with a suspension of organisms containing mineral oil. Animals were examined monthly by histopathology and bacterial tissue counts of liver and spleen over a 6-month period. Only Balb/c mice maintained a steady infection with an average of 4.1 x 10 5 ± 7.8 x 10 3 and 8.1 x 10 5 ± 2 .6 x 10 4 colony forming units (cfu) per gram of liver and spleen, respectively, during the course of the study. In contrast, C57/1310 mice reduced the bacterial counts in the liver and spleen from 6.8 x 10 4 and 1.3 x 10 5 to 7.1 x 102 and 4.3 x 1O 3, respectively during the first 120-150 clays after infection. The reduction in cfu was associated with the development of caseous necrotic lesions. C57/B10 mice were of intermediate resistance, slowly reducing cfu in the liver, but not the spleen, during the 6-month period. Balb/c was found to be a suitable mouse strain fiar the study of chronic M. paratuberculosis infection.