Legionella pneumophila appearance
- thin, Gram-negative bacteria; Legionella stains poorly with Gram stain; may become filamentous in culture
- motile (one polar flagellum)
Infections caused by Legionella pneumophila
Legionnaires' disease (also legionellosis or Legion fever) is a form of atypical pneumonia caused by any species of Gram-negative aerobic bacteria belonging to the genus Legionella. Over 90% of cases of Legionnaires' disease are caused by Legionella pneumophila.
L. pneumophila has only been found in aquatic systems, where it is symbiotically present in aquatic-borne amoebae. It thrives in temperatures between 25 and 45°C , with an optimum temperature of 35°C. During infection, the bacterium invades macrophages and lung epithelial cells and replicates intracellularly.
Legionnaires' disease is transmitted by inhalation of aerosolized water. It is not airborne and it is not transmitted from person to person. Sources where temperatures allow the bacteria to thrive include hot-water tanks, cooling towers, and evaporative condensers of large air-conditioning systems, such as those commonly found in hotels and large office buildings (Wikipedia).
Legionella pneumophila can also cause Pontiac fever, an acute, non-fatal respiratory disease caused by various species of Gram-negative bacteria in the genus Legionella. It is a mild upper respiratory infection that resembles acute influenza. Pontiac fever resolves spontaneously and often goes undiagnosed (Wikipedia)..