Anthrax bacteria. Light micrograph of anthrax bacteria (Bacillus anthracis). These rod-shaped Gram-positive bacteria are highly pathogenic. Commonly a livestock infection, anthrax is passed to humans by contact with contaminated animal hair, hides or excrement. The bacteria can also remain dormant in the soil for many years within spores. The disease comes in two forms: pulmonary and cutaneous anthrax. The latter causes a boil to form at the site of the bacteria's entry and can be cured with prompt antibiotic treatment. Pulmonary anthrax, however, is fatal in most cases. Phase contrast. Magnification: x500 at 35 mm size.