Legionella pneumophila: an aquatic microbe goes astray

Abstract

Legionella pneumophila is naturally found in fresh water were the bacteria parasitize within protozoa. It also survives planctonically in water or biofilms. Upon aerosol formation via man-made water systems, L. pneumophila can enter the human lung and cause a severe form of pneumonia, called Legionnaires' disease. The pathogenesis of Legionnaires' disease is largely due to the ability of L. pneumophila to invade and grow within macrophages. An important characteristic of the intracellular survival strategy is the replication within the host vacuole that does not fuse with endosomes or lysosomes. In recent times a great number of bacterial virulence factors which affect growth of L. pneumophila in both macrophages and protozoa have been identified. The ongoing Legionella genome project and the use of genetically tractable surrogate hosts are expected to significantly contribute to the understanding of bacterium-host interactions and the regulation of virulence traits during the infection cycle. Since person-to-person transmission of legionellosis has never been observed, the measures for disease prevention have concentrated on eliminating the pathogen from water supplies. In this respect detection and analysis of Legionella in complex environmental consortia become increasingly important. With the availability of new molecular tools this area of applied research has gained new momentum.

Legionella pneumophila in the Environment: The Occurrence of a Fastidious Bacterium in Oligotrophic Conditions

“…Table 1 gives an overview of some of the media used to culture Legionella pneumophila. The fastidious nature in axenic cultures is contradictory to the nutritionally poor environment in which the bacterium is often detected (Steinert et al 2002).…”

“…Furthermore, L. pneumophila has a fascinating ecology as intracellular parasite of various freeliving freshwater protozoa (Abu . They are also known to persist in biofilms which develop in building water systems, either with or without these protozoa (Rogers et al 1994A;Fields 1996;Fliermans 1996;Murga et al 2001;Steinert et al 2002;van der Kooij et al 2002). The survival in biofilms is discussed below.…”

“…Since person-toperson transmission has never been observed, the control measures to prevent the bacterium from spreading usually focus on the elimination of the pathogen from water installations. In this respect, the detection and analysis of L. pneumophila in complex environmental consortia have become increasingly important (Fields 1996;Steinert et al 2002).…”

“…naturally infecting protozoa. Although it is now generally accepted that L. pneumophila primarily exist within biofilms, only a limited number of studies have attempted to characterise the interaction of the bacterium within these complex matrices (Fields 1996;Fliermans 1996;Steinert et al 2002). Most recent studies pay attention to the pathogenesis, the epidemiology, the clinical microbiology and some molecular aspects of L. pneumophila, rather than to the ecology of the bacterium.…”

“…The survival or growth of L. pneumophila probably depends on the influence of its partners and opponents, since the pathogen mostly persists in microbial hotspots such as multispecies biofilms (Rogers et al 1994A;Fields 1996;Fliermans 1996;Murga et al 2001;Steinert et al 2002). The relation between biofilm formation and the multiplication of L. pneumophila has not yet been quantified and the prevention or abatement of biofilm formation has attracted limited attention as a control measure.…”