L. PNEUMOPHILA AND LEGIONNAIRES' DISEASE
Legionella pneumophila is a Gram-negative facultative intracellular pathogen capable of growing in both protozoan and mammalian host cells. L. pneumophila is found in natural and artificial water reservoirs and less often in soil and organic matter (Fields, 1996; Szymanska et al., 2004). Optimal proliferation conditions for Legionella are those in which water temperatures are between 25°C and 42°C, calcium and magnesium salt-containing sediments are present, and are further enhanced by the presence of algae and protozoa (Szymanska et al., 2004). In hostile conditions, Legionella and other organisms become attached to surfaces in an aquatic environment, forming a biofilm (Langmark et al., 2005). L. pneumophila can be isolated from such natural water sources as lakes, ponds and streams; however, artificial reservoirs such as plumbing fixtures, hot water tanks, whirlpool spas and cooling towers, all possess excellent conditions for Legionella proliferation inside protozoan hosts and are the source of most outbreaks (Fliermans et al., 1981; Yee and Wadowsky, 1982).
The first recognized outbreak of L. pneumophila occurred in Philadelphia in 1976 during a state convention of the American Legion (Fraser et al., 1977). During this outbreak a total of 221 people contracted the disease, 34 of whom subsequently died. A new Gram-negative bacterium was isolated from both patients and the air-conditioning system of the hotel that was the source of the outbreak (McDade et al., 1977). This isolated organism was named Legionella pneumophila (Brenner et al., 1979). There are 48 different species of Legionella found in nature.
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