Bacillus species are rod-shaped, endospore-forming aerobic or facultatively anaerobic, Gram-positive bacteria; in some species cultures may turn Gram-negative with age. The many species of the genus exhibit a wide range of physiologic abilities that allow them to live in every natural environment. Only one endospore is formed per cell.
The spores are resistant to heat, cold, radiation, desiccation, and disinfectants. Bacillus anthracis needs oxygen to sporulate; this constraint has important consequences for epidemiology and control. In vivo, B anthracis produces a polypeptide (polyglutamic acid) capsule that protects it from phagocytosis. The genera Bacillus and Clostridiumconstitute the family Bacillaceae. Species are identified by using morphologic and biochemical criteria.
Diseases caused by bacilli-shaped bacterium include the following: tuberculosis (TB), whooping cough, tetanus, typhoid fever, diphtheria, salmonellosis (see Salmonella), shigellosis, legionnaires’ disease, and botulism.