Virulence of Mycobacterium avium complex strains from acquired immune deficiency syndrome patients: relationship with characteristics of the parasite and host

The virulence of 24 strains of Mycobacterium avium complex (MAC) isolated from patients with acquired immune deficiency syndrome (AIDS) was assessed using the beige mouse model. Most changes in colony forming unit (cfu) counts in spleen and lungs, and spleen weights occurred between days 1 and 14, with comparatively smaller changes 14-28 days postinfection. The virulence was assessed by a score formulated from the four most useful parameters: mortality, spleen cfu, lung cfu and spleen weights at 28 days. The scores of the 24 strains showed a normal distribution; four strains falling above one standard deviation from the mean were classified as high virulent, those four falling below one standard deviation as low virulent, and the remaining 16 as of intermediate virulence. Virulence was associated with the total number of plasmids and the occurrence of large plasmids (greater than 100 MDa) in the MAC strains. There was an inverse correlation between virulence and the organism's capacity to trigger the release of oxygen metabolites from peritoneal macrophages. Macrophages from mice infected with the MAC strains of different degrees of virulence released superoxide anion (O2-) with a peak at two weeks, the peak levels bearing an inverse correlation to virulence. No association was seen between virulence and source of specimens, biochemical characteristics, drug susceptibility, serotypes or phage types.

Susceptibility of beige mice to Mycobacterium avium complex infections by different routes of challenge

We have studied the susceptibility of beige (C57Bl/6/bgJ/bgJ) mice to a virulent strain of Mycobacterium avium complex (MAC) (101) by intravenous, intraperitoneal, intranasal, oral, and intrarectal routes. Consistent with our earlier findings, intravenous challenge resulted in high mortality and colony-forming unit (CFU) counts of recoverable organisms from spleens, lungs, livers, and lymph nodes, plus high levels of mortality. Intraperitoneal challenge resulted in high organ CFU counts but no mortality. Of relevance to the sexual practice of certain homosexual patients with AIDS is the intrarectal route of inoculation, which resulted in extensive involvement of the visceral organs with MAC disease. Multiple challenges by intravenous, oral, or rectal routes resulted in higher CFU counts than did single exposures.

In vivo activity of amikacin alone or in combination with clofazimine or rifabutin or both against acute experimental Mycobacterium avium complex infections in beige mice

The in vivo activity of amikacin, used alone or in combination with rifabutin or clofazimine or both, was assessed in the treatment of early and established Mycobacterium avium complex infections in beige mice. Amikacin given alone at a dose of 50 mg/kg, in one, two, or three divided doses, showed remarkable activity. Addition of clofazimine increased the activity significantly, but addition of the third drug, rifabutin, did not further improve the results. Amikacin-containing regimens are worthy of consideration for investigations in patients with M. avium complex infections.