LEGIONELLA - World Health Organization

L. pneumophila is thermotolerant and able to withstand temperatures of 50 °C for several hours.
The identification of Legionella spp. in hot-water tanks or in thermally polluted rivers emphasizes
that water temperature is a crucial factor in the colonization of water distribution systems
(Yu, 2000), the proliferation of legionellae in the environment, and therefore the risk of Legionella
infection. Maintaining the temperature of hot and cold-water systems within buildings to
prevent or minimize the growth of legionellae is an important control measure to prevent the
risk of Legionella infection.
2.2.2 Effect of other microorganisms
Requirement for nutrients
Water alone is insufficient to allow L. pneumophila to proliferate; for example, in studies using
sterile distilled water and sterile tap water, L. pneumophila survived in the long term but did
not multiply (Skaliy & McEachern, 1979; Fields et al., 1984). Other microorganisms allow
Legionella to amplify; for example, naturally occurring L. pneumophila were able to survive
and multiply in non-sterile tap water (Yee & Wadowsky, 1982). In continuous-culture model
systems seeded with a mixed microflora from a potable water system, L. pneumophila grew
when fed solely with filtered, sterilized drinking water for prolonged periods (Lee & West,
1991; Rogers et al., 1994). These results suggest that growth of Legionella requires nutrients
already available in the tap water. The nutrients may be supplied, directly or indirectly, by other
species of bacteria or other associated microorganisms in the form of dissolved organic constituents,
through the excess production of organic nutrients or through decay of the microorganisms
(Tesh & Miller, 1981; Yee & Wadowsky, 1982; Stout, Yu & Best, 1985):
These results are consistent with studies showing that amino acids are the main nutrient
requirement for L. pneumophila growth (Pine et al., 1979; Warren & Miller, 1979; Wadowsky
& Yee, 1985).
The association of L. pneumophila with many different microorganisms from aquatic sources has
been demonstrated; the microorganisms include protozoa, Fischerella spp. and other bacteria
(Fliermans et al., 1981; Tesh & Miller, 1981; Bohach & Snyder, 1983; Wadowsky & Yee, 1983;
Wadowsky & Yee, 1985; Rowbotham, 1986; Grimes, 1991).
Protozoa
Drozanski (1963) described bacterial parasites of amoebae that had been isolated from soil
but failed to grow on laboratory media. It is possible that these bacterial parasites were Legionella
spp. Rowbotham (1980) was the first to report the relationship between amoebae and
L. pneumophila; it has subsequently been confirmed that legionellae are facultative intracellular
parasites. (Facultative organisms are those that are able to grow in altered environmental conditions,
for example, in the presence or absence of a specific environmental factor, such as oxygen.)
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS