Legionella is a genus of Gram-negative bacteria that can be seen using a silver stain or grown in a special media that contains cysteine, an amino acid. Most Legionella species are intracellular pathogens whose primary hosts are amoebae, however many Legionella are accidental pathogens of humans. Legionella bacteria are known to cause legionellosis including a pneumonia-type illness called Legionnaires' disease and a mild flu-like illness called Pontiac fever. These bacteria are common in many places, like soil and water. Legionella are aerobic and motile. There are over 50 species and 70 types (serogroups) identified. Legionella does not spread from person-to-person. Most individuals who are exposed to the bacteria do not get sick. Most outbreaks result from poorly maintained cooling towers.