Legionella

The Legionellae are bacteria belonging to the Legionellagenus.

Characteristics of Legionellae

Legionella was discovered in 1977, and is a Gram negative bacillus with polar flagella. They are facultative intracellular bacilli which can colonise amoebae in aquatic environments or animal cells. They are also occasionally found in cooling towers and hot water systems.

Legionella has a 3.5 million base pair genome which is a circular chromosome and codes for approximately 3,200 proteins.

Legionella and the legionelloses

The bacteria are inhaled by human beings through water droplets. After reaching the pulmonary alveoli the Legionella enter macrophages and destroy them. The pathogenicity (pneumonia) is cased by this cell lysis triggered by bacterial virulence factors.

The Legionella genus contains around fifty species in which some cells are broken down into several tens of serogroups. More than 90% of the cases found however are due to Legionella pneumophilaalone. L. longbeachae is associated with 30.4% of cases of legionellosis in Australia and New Zealand.