Antimicrobial activities of levofloxacin, clarithromycin, and KRM-1648 against Mycobacterium tuberculosis and Mycobacterium avium complex replicating within Mono Mac 6 human macrophage and A-549 type II alveolar cell lines.

The antimicrobial activities of levofloxacin, clarithromycin and KRM-1648 against Mycobacterium tuberculosis (MTB) and Mycobacterium avium complex (MAC) residing in Mono Mac 6 human macrophage-like cells (MM6-Mphis) and A-549 human type II alveolar epithelial cells (A-549 cells) were studied. We measured the antimicrobial activity of test drugs in terms of effects on the behaviour of intracellular organisms during a 7-day cultivation of MTB- or MAC-infected cells in the medium containing the drugs at Cmax doses. Microbicidal action of levofloxacin against intracellular MTB within A-549 cells was markedly less than its activity against the same organisms in MM6-Mphis. The same effect was also noted for the action of KRM-1648 against MAC organisms but this did not occur with clarithromycin. The MIC of KRM-1648 for MAC multiplying within A-549 cells was 32 times larger than that for MAC residing in MM6-Mphis. These findings indicate that MTB and MAC organisms replicating in the type II lung epithelial cells resist the action of certain antimycobacterial agents such as quinolones and rifamycin derivatives but not when the organisms are contained in macrophages. It appears that the antimicrobial action of certain drugs against intracellular mycobacteria is differentially manifested depending on the types of host cells, i.e. professional phagocytes (MM6-Mphis) or non-professional phagocytes (A-549cells), in which the organisms are contained.