Bacillus anthracis endospores are seen under phase contrast microscopy. Bacillus anthracis is a gram-positive, endospore-forming, rod-shaped bacterium. Their spores can live for many years which, enables the bacteria to survive in a dormant state. Anthrax is an acute disease caused by the bacterium Bacillus anthracis. Most forms of the disease are lethal, and it affects both humans and other animals. There are effective vaccines against anthrax, and some forms of the disease respond well to antibiotic treatment. When spores are inhaled, ingested, or come into contact with a skin lesion on a host, they may become reactivated and multiply rapidly. Anthrax spores can be produced in vitro and used as a biological weapon. Anthrax does not spread directly from one infected animal or person to another; it is spread by spores. Bacillus anthracis bacterial spores are soil-borne.