Comparison of the Resistance of C57BL 6 and C3H He Mice to infection with Mycobacterium paratuberculosis

Susceptibility of C57BL 6 (Bcg^s) and C3H HeN (Bcg^r) mice to an intraperitoneal infection with Mycobacterium paratuberculosis strain 19698 was compared (by histopathology and the number of mycobacteria isolated from the spleen). Mycobacterial counts from the spleen of Bcg^r mice progressively decreased over the course of infection but remained unchanged in Bcg^s mice. Granulomatous lesions and acid-fast bacteria were consistently present in the liver and lymph nodes of Bcg^s mice, whereas lesions were transient or absent in Bcg^r mice. These results indicate that Bcg^r mice are inherently resistant to M. paratuberculosis, whereas Bcg^s mice are inherently susceptible. These differences may prove useful in elucidating the mechanisms of resistance and susceptibility to paratuberculosis and other mycobacterial infections.