Comparison of the Virulence for Mice of Mycobacterium avium and Mycobacterium intracellulare Identified by DNA Probe Test

The virulence of various serovars of Mycobacterium avium and M. intracellulare identified by DNA probe test was compared with each other. We found species- and serovar-dependencies of M. avium complex (MAC) virulence to mice in terms of mortality, incidence of lung lesions and bacterial load in the visceral organs, as follows. First, human- or environment-derived M. intracellulare was more virulent for mice, as compared to M. avium isolated from patients or environmental sources. Second, the virulence of MAC isolates belonging to serovars 1, 8, 9 (M. avium), 14 and 16 (M. intracellulare) is in the order of serovars 16>14>8>1>9. These aspects were different from those for MAC virulence to human and bird, swine and cattle.