Experimental murine infections with a Mycobacterium avium-intracellulare complex organism isolated from mice

B6C3F1 hybrid mice did not develop lesions of mycobacterial infection when intratracheally inoculated with a Mycobacterium avium-intracellulare complex organism isolated from a naturally occurring outbreak among C57BL/6N mice in a B6C3F1 hybrid production colony. Young C57BL/6N females did not develop lesions when comingled with naturally infected adult C57BL/6N mice. After subcutaneous or oral inoculation of the isolate into 8-week-old and adult 36- to 40-week-old C57BL/6N mice, it was found that the subcutaneous route yielded a higher percentage of culture positive lungs and animals with gross and microscopic pulmonary lesions than the oral route of inoculation. Adult mice were more susceptible to infection than 8-week-old animals.