Anthrax bacteria. Computer artwork of Bacillus anthracis bacteria (green) releasing spores (orange). These are Gram-positive, rod-shaped, spore-forming bacteria. The spores are reproductive cells that are able to survive dormant in unfavourable conditions for long periods of time. B. anthracis is the cause of anthrax. It can infect the skin (cutaneous anthrax), causing raised itchy lesions, the lungs (pulmonary anthrax), which is fatal unless treated quickly, and the digestive system (gastrointestinal anthrax), causing vomiting of blood and severe diarrhoea. All forms can be fatal if left untreated. Treatment is with antibiotics.