Germination of Bacillus anthracis spores within alveolar macrophages

Abstract

SummaryThe fatal character of the infection caused by inhalation of Bacillus anthracis spores results from a complex pathogenic cycle involving the synthesis of toxins by the bacterium. We have shown using immunofluorescent staining, confocal scanning laser microscopy and image cytometry analysis that the alveolar macrophage was the primary site of B. anthracis germination in a murine inhalation infection model. Bacillus anthracis germinated inside murine macrophage-like RAW264.7 cells and murine alveolar macrophages. Germination occurred in vesicles derived from the phagosomal compartment. We have also demonstrated that the toxin genes and their trans-activator, AtxA, were expressed within the macrophages after germination.

Poly-γ-Glutamate Capsule-Degrading Enzyme Treatment Enhances Phagocytosis and Killing of EncapsulatedBacillus anthracis

“…Germinated spores and bacilli are thought to eventually escape from the macrophage into the lymph nodes and then the bloodstream, where they spread systemically to most organs and replicate virtually unimpeded as short chains of phagocytosis-resistant encapsulated bacilli. Evidence suggests that the toxins (19) and capsule (15) are synthesized early after germination. The lethal and edema toxins are thought to interfere with macrophage function, although their role in intracellular killing and the fate of B. anthracis itself in macrophages remain unclear, with either killing (60), persistence (18), or growth (10) being reported, which is likely related to methodological differences and the use of different cells and bacterial strains, both encapsulated and unencapsulated.…”

In-vitro characterisation of the phagocytosis and fate of anthrax spores in macrophages and the effects of anti-PA antibody

“…However, several steps in the process have been delineated or hypothesised based on observations in animals and in in-vitro model systems [21][22][23][24][25][26][27][28]. Upon inhalation of a lethal dose of B. anthracis spores by a susceptible host, such as a guinea-pig, the spores appear to be taken up by cells lining the alveoli and by free phagocytes [26,28].…”

Early Bacillus anthracis-macrophage interactions: intracellular survival and escape

“…To assess co-localization of germinated B. anthracis endospores with the phagolysosome (Guidi-Rontani et al, 1999) and their subsequent escape into the cytoplasm, fluorescence microscopy of Texas Red±ovalbumin-labelled Mf was utilized (Steinberg and Swanson, 1997). Bone marrow-derived macrophages were used because they are flat, allowing optimal resolution during phase and epifluorescence microscopy.…”

“…The exact manner by which B. anthracis survives the Mf and how it escapes remain unknown. However, as vegetative anthrax bacilli co-localize with phagolysosomal markers (Guidi-Rontani et al, 1999), the first two strategies of subcellular survival seem unlikely. The genes and factors responsible for this early establishment stage may comprise novel anthrax virulence factors that have yet to be described.…”