Molecular and cellular characterization of the intracellular phenotype of Mycobacterium avium.

摘要

Mycobacterium avium cause disseminated disease in immunocompromised people such as AIDS patients. Subsequent to crossing the intestinal epithelium, M. avium thrive within vacuoles in macrophages. The bacteria exhibit a different, more invasive, phenotype after being in macrophages compared to M. avium from laboratory conditions. We hypothesized that this intracellular phenotype contributes to disease in a variety of ways, such as influencing apoptosis of the macrophage. We further studied this intracellular phenotype, analyzing the molecular and cellular details. Using microscopy, we found that a portion of M. avium survive after the macrophage becomes apoptotic. From apoptotic bodies, some bacteria were observed escaping the vacuole and macrophage to the extra-cellular space and others were seen invading the macrophage ingesting the apoptotic body. We also found that macrophages infected by M. avium undergo autophagy, and that bacteria from autophagic macrophages were viable. After developing an in vitro system that elicits the intracellular phenotype, we determined that macrophages infected by bacteria exhibiting the intracellular phenotype undergo early-onset cell-death frequently compared to macrophages infected by bacteria exposed to laboratory conditions. With the use of real time PCR and microarray analysis, several genes, including genes of the twin-arginine translocase system, were shown to be upregulated by bacteria with the intracellular phenotype, while others were downregulated. The twin-arginine translocase system of M. avium was further characterized, and a tatb antisense strain was found to enter and survive in macrophages more efficiently than the wildtype strain, but was more sensitive to beta-lactam antibiotics. Finally, we analyzed four transposon mutants of M. avium that were impaired in their ability to be taken up by macrophages to determine if the vacuole in which they reside, an aspect partially controlled by the bacteria, and therefore a part of the intracellular behavior of M. avium, differs from the vacuole containing wildtype bacteria. Some of these mutants were found in vacuoles with marked difference compared to the wildtype-containing vacuoles, others were similar to the wildtype. This work has increased our understanding of the intracellular phenotype of M. avium and how it may contribute to aspects of disease such as cell-to-cell spread.