Legionella (Legionella) is a genus of rod-shaped bacteria of the family Legionellaceae. They are aquatic Gram-negative non-sporulating bacteria, motile by one or more polar or subpolar flagella. Legionella are considered potentially pathogenic to humans. At present, more than 48 species and 70 serogroups are known. The most important for human diseases is Legionella pneumophila (about 70 to 90%, depending on the region), it is the agent of Legionellosis or Legionnaire’s disease.

A special feature of many species of the genus Legionella is the high proportion of branched fatty acid chains in their membrane lipids. For example, in Legionella pneumophila the proportion of branched chains is 64%.

Legionella consists to a large extent of fatty acid chains

Fatty acid chain share


  • Hot water production and distribution systems
  • Swimming pools
  • Air washers in air conditioners
  • Cooling towers
  • Biofilms
  • Hospitals
  • School and other public showers
  • Bath and ward baths
  • Dead pipes
  • Water tanks
  • Cold water supply lines to thermal mixers


Transmission of Legionella is principally possible through contact with tap water when the Legionella enter the deep lung sections.

Not every contact with legionella-containing water leads to a health hazard. Only inhalation of bacteria-containing water as an aerosol (aspiration or inhalation, for example during showering, in air conditioners, through lawn sprinklers and in whirlpools) can lead to infection.

Drinking legionella-rich water is not a health hazard for people with intact immune systems.

Transmission of legionellosis is particularly associated with the following technical systems:

Hot water supplies (for example, in homes, hospitals, homes, hotels), air conditioning systems (air conditioning) and humidifiers

Baths, in particular hot springs (whirlpools),as well as other installations that atomize water into water droplets (for example fog generators, fog wells).