Legionella
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Legionella is a genus of rod-shaped bacteria belonging to the family Legionellaceae. They are aquatic Gram-negative and non-spore-forming bacteria that are motile by one or more polar or subpolar flagella (flagella). Legionella are considered potentially pathogenic to humans. Currently, more than 48 species and 70 serogroups are known. The most significant species for human diseases is Legionella pneumophila (share of about 70 % to 90 %, depending on the region), it is the causative agent of legionellosis or Legionnaires' disease.
A special feature of many species of the genus Legionella is the high proportion of branched fatty acid chains in their membrane lipids. In Legionella pneumophila, for example, the proportion of branched chains is 64 %.
Living Conditions
The optimal living conditions for legionella are:
- Fresh and salt water
- Fresh water replenishment
- long dwell time
- Temperature range 25 °C to 50 °C
Effects of different temperature ranges on the proliferation of Legionella:
| Temperature range | Effect on the reproduction rate |
| up to 20 °C | very slow reproduction |
| at 20 °C and above | multiplication rate |
| 30 °C to 45 °C | optimal reproduction |
| from 50 °C | hardly any increase |
| from 55 °C | no longer possible |
| from 60 °C | Killing of legionella |
A study by the Helmholtz Centre for Infection Research (HZI) in Braunschweig has shown that the bacterial pathogen Legionella pneumophila also multiplies at water temperatures between 50 and 60 °C. The researchers believe that further studies should clarify the consequences of this for the management of hot water systems, air conditioning systems and cooling towers. According to the researchers, the consequences of this for the management of hot water systems, air conditioning systems and cooling towers should be clarified by further studies.
Occurrence of legionella
Legionella are found where warm water offers optimal conditions for their reproduction. They are viable in the temperature range from 5 °C to 55 °C; above 60 °C they become inactive after a few minutes. Corresponding conditions can exist, for example, in
- Hot water production and distribution systems
- Water tanks and boilers
- Cold water supply lines with long downtimes (e.g. after a long holiday or moderately used fire extinguishing lines with drinking water connection)
- Cold water supply lines with heat effect from outside or to thermostatic mixers
- Deadlines
- Swimming pools
- Hospitals
- public showers (e.g. school showers)
- Baths and ward baths
- Air washers of air conditioning systems
- Cooling towers
- Biofilms
Questions and Answers
Q: What is Legionella?
A: Legionella is a genus of Gram-negative bacteria that is pathogenic and includes species causing Legionnaires' disease and Pontiac fever.
Q: What illnesses can Legionella cause?
A: Legionella can cause Legionnaires' disease, a pneumonia-type illness, and a mild flu-like illness called Pontiac fever.
Q: Where is Legionella commonly found?
A: Legionella is common in many environments including soil and aquatic systems, with at least 50 species and 70 strains identified.
Q: How are Legionella bacteria classified serologically?
A: The somatic or O antigen determinants on Legionella bacteria are used for serologically classifying them, which is determined by the chemical composition of sugar and their arrangement.
Q: Why was Legionella named so?
A: Legionella is named after the outbreak of an unknown "mystery disease" that occurred in 1976 which sickened 221 people with 34 deaths, first noticed among people attending an American Legion convention. The cause was later identified as Legionella.
Q: What is the significance of Legionella being Gram-negative bacteria?
A: Legionella being Gram-negative bacteria means that they have an outer membrane that makes them more resistant to antibiotics and other environmental factors.
Q: Is Legionella contagious between humans?
A: Legionella is not contagious between humans, rather it is spread through the inhalation of contaminated aerosols or mist from water systems.
