Legionella

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. It is known to cause legionellosis (all illnesses caused by Legionella) 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. 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.

The cell wall of the Legionella bacteria has parts that determine its specific type. The structural arrangement and building blocks (sugars) in the cell wall help classify the bacteria.

Etymology

Legionella was named after a 1976 outbreak of a then-unknown "mystery disease" at a convention of the American Legion, an association of U.S. military veterans, in Philadelphia. This outbreak happened within days of the 200th anniversary of the signing of the Declaration of Independence, which led to it being highly publicized and caused great concern in the U.S. On January 18, 1977, the causative agent was identified as a previously unknown bacterium subsequently named Legionella.

Detection

The detection of Legionella typically requires growing them on buffered charcoal yeast extract agar. As Legionella growth requires cysteine and iron, it cannot grow on other common lab media.

To detect Legionella in water, it is first concentrated, then inoculated into charcoal yeast extract agar containing selective agents that prevent the growth of other organisms. Heat or acid treatments are sometimes used to eliminate other microbes in a sample.