Anthrax Infection of an Immune Cell

Bacillus anthracis is a gram-positive spore-forming bacterium and is the causative agent of inhalational anthrax. This complex disease begins with the inhalation of the dormant spore-form of the bacterium which facilitates deposition of the spores in the alveoli of the lung. The spores remain dormant in the lung and are engulfed by resident immune cells and transported across the alveolar epithelium and into the systemic circulation and lymphatics. The spores then germinate within the immune cells, burst out of the cells and replicate to high numbers within the systemic circulation which ultimately leads to death of the host. In this regard, the bacterium uses the immune cell as a “Trojan Horse” to cross the epithelium and gain access to the bloodstream. Our research is aimed at elucidating the initial interactions between Bacillus anthracis and immune cells such as macrophages and dendritic cells. We label B. anthracis spores with a fluorescent dye and then incubate them in the presence of human-derived macrophages. After 2-4 hours, we stain the actin cytoskeleton and the nuclear DNA of the macrophage with red and blue dyes, respectively and then image the cells by fluorescence microscopy. This enables us to visualize the spores within the macrophage and determine the mechanism by which they interact with the human cells. The image that I have submitted was captured on a Delta Vision RT microscope within our laboratory in the department of microbiology. The image shows three Bacillus anthracis spores within a human-derived macrophage.