Some species are natural flora in the human intestines.
When grown on blood agar, Bacillus produces large, spreading, gray-white colonies with irregular margins. A unique characteristic of this bacterium is its ability to produce endospores when environmental conditions are stressful. Anthrax is transmitted to humans via direct contact with animal products or inhalation of endospores. Under the microscope, B. anthracis cells appear to have square ends and seem to be attached by a joint to other cells. The spores are best observed when the bacterium is cultured on artificial media.