Chapter Eight - Legionella

Abstract

Legionella is the sole genus of the family Legionellaceae. It is composed of many species and serogroups and following 16S rRNA analysis it now belongs to the gamma-2 subgroup of the class Proteobacteria. Legionellae have an absolute requirement for iron and utilize amino acids for energy rather than carbohydrates. Legionellosis occurs following inhalation of aerosolized droplets of Legionella. Once inhaled, the organism then attaches to alveolar macrophages. Legionellae are then phagocytosed by these macrophages. Virulent strains of Legionella are able to multiply inside macrophages as they are able to inhibit the fusion of phagosomes with lysosomes. Macrophage invasion protein (MIP) and an integral protein are thought to be the main virulence factors for Legionella. Legionella causes legionellosis, which has two forms: Pontiac fever and Legionnaires' disease. Legionellae can be detected using swab samples from biofilms within water systems, suggesting a survival strategy for the organism in biofilms. Disinfection reduces levels of Legionella in water systems. However, long-term elimination from aquatic environments has not been possible, even in chlorinated systems