Bacteria Genomes - LEGIONELLA PNEUMOPHILA

The first discovery of bacteria from genus Legionella was in 1976 when an outbreak of pneumonia at an American Legion convention led to 29 deaths. The causative agent, what would come to be known as Legionella pneumophila, was isolated and given its own genus. The organisms classified in this genus are Gram-negative bacteria that are considered intracellular parasites.

Legionella pneumophila is a motile, rod-shaped, gram-negative, aerobic, bacterium. It requires complex nutritional requirements such as high cysteine levels and low sodium levels to grow. Legionella pneumophila have always been found in non-marine aquatic environments such as lakes and ponds. The optimum growth temperature range for this bacteria is 20-45 degrees Celsius. It thrives in areas where there are high concentrations of rust, algae, and organic particles, as these supply the bacteria with a source of iron as well a nitrogen. These are necessary for providing nutrients for growth, as well as protection from harsh chemicals. The organism has been found to possess the ability to survive in tap water at room temperature for over a year.

Legionella, in their natural environments, grow within other organisms. For example, the bacteria have frequently been found to be in very close association, possibly an endosymbiotic relationship, with certain protozoan. Hartmanella vermiformis, Tetrahymena thermophila, and Acanthamoeba castellani are just a few of the protozoa that have been identified to have Legionella growing within them. The reason why Legionella grow inside these amoebae is because the bacteria multiply intracellularly, and therefore require the amoebae to aid in reproduction. It has been determined that one amoebae can house enough Legionella bacteria to infect a human being, and this single amoebae is small enough to fit in one droplet of aerosolised water.

Legionella bacteria are transmitted to the lungs of human beings through a process called aerosilisation. The most common devices that have been found to transmit the bacteria are air conditioning cooling towers, however, there are many other devices that can transmit the bacteria.

Infection by Legionella pneumophila results mainly in Legionnaire's Disease. However, some strains of the bacteria have been known to manifest a disorder called Pontiac Fever. This is a very mild infection which causes influenza-like symptoms and will go away without treatment. Incidence of Legionellosis or Legionnaire's Disease have increased over the past decade or so because of the use of central air conditioning, especially in office buildings, hotels, and hospitals.

The first symptoms of Legionnaires Disease are noticed anywhere within two to ten days post-infection. On average, however, its usual incubation is about five to six days. It is primarily characterised by a bacterial pneumonia. Initially, however signs such as anorexia, malaise, myalgia, and headache should concern doctors of the possibility of infection by the Legionella bacterium . Other more specific symptoms of this disease are: nonproductive cough, high fever with chills, abdominal pain, vomiting and diarrhea.

The major side-effect of Legionnaire's Disease is is respiratory failure which requires mechanical ventilation. Other complications are acute renal failure, hypotension, and shock. In hospitalised patients the most recent case fatality rate has been determined to be fifteen percent.

References:

Science 305(5692):1966-1968 (2004)
http://medic.med.uth.tmc.edu/path/00001507.htm
http://genome3.cpmc.columbia.edu/~legion/