Anthrax bacteria. Light micrograph of a section through tissue infected with anthrax bacteria, Bacillus anthracis (blue). These Gram-positive rod-shaped (bacilli) 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. In cutaneous anthrax, a boil forms at the site of the bacteria's entry. This disease can be cured with prompt antibiotic treatment. Pulmonary anthrax, however, is fatal in most cases. Phase contrast. Magnification: x400 at 35 mm size.