My watch list  



Legionella sp. under UV illumination.
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gamma Proteobacteria
Order: Legionellales
Family: Legionellaceae
Genus: Legionella
Brenner et al. 1979

Legionella adelaidensis
Legionella anisa
Legionella beliardensis
Legionella birminghamensis
Legionella bozemanii
Legionella brunensis
Legionella busanensis
Legionella cherrii
Legionella cincinnatiensis
Legionella donaldsonii
Legionella drancourtii
Legionella drozanskii
Legionella erythra
Legionella fairfieldensis
Legionella fallonii
Legionella feeleii
Legionella geestiana
Legionella genomospecies 1
Legionella gratiana
Legionella gresilensis
Legionella hackeliae
Legionella impletisoli
Legionella israelensis
Legionella jamestowniensis
'Candidatus Legionella jeonii'
Legionella jordanis
Legionella lansingensis
Legionella londiniensis
Legionella longbeachae
Legionella lytica
Legionella maceachernii
Legionella micdadei
Legionella moravica
Legionella nautarum
Legionella oakridgensis
Legionella parisiensis
Legionella pneumophila
Legionella quateirensis
Legionella quinlivanii
Legionella rowbothamii
Legionella rubrilucens
Legionella sainthelensi
Legionella santicrucis
Legionella shakespearei
Legionella spiritensis
Legionella steigerwaltii
Legionella taurinensis
Legionella tucsonensis
Legionella wadsworthii
Legionella waltersii
Legionella worsleiensis
Legionella yabuuchiae

Legionella is a Gram negative bacterium, including species that cause legionellosis or Legionnaires' disease, most notably L. pneumophila.[1] Legionella are common in many environments, with at least 50 species and 70 serogroups identified. The side-chains of the cell wall carry the bases responsible for the somatic antigen specificity of these organisms. The chemical composition of these side chains both with respect to components as well as arrangement of the different sugars determines the nature of the somatic or O antigen determinants, which are essential means of serologically classifying many Gram-negative bacteria.



Legionella is traditionally detected by culture on buffered charcoal yeast extract (BCYE) agar. Legionellae require the presence of cysteine to grow and therefore do not grow on common blood agar media used for laboratory based total viable counts or on site displides. Common laboratory procedures for the detection of Legionella in water[2] concentrate the bacteria (by centrifugation and/or filtration through 0.2 micron filters) before innoculation onto a charcoal yeast extract agar containing antibiotics (e.g. glycine vancomycim polymixin cyclohexamide, GVPC) to suppress other flora in the sample. Heat or acid treatment are also used to reduce interefernece from other microbes in the sample.

After incubation for up to 10 days, suspect colonies are confirmed as Legionellae if they grow on BCYE containing cysteine, but not on agar without cysteine added. Immunological techniques are then commonly used to establish the species and/or serogroups of bacteria present in the sample.

New techniques for the rapid detection of Legionella in water samples are emerging including the use of polymerase chain reaction (PCR)[3] and rapid immunological assays[4]. These technologies can typically provide much faster results.


Legionella have been known for some time to live within amoebae in the natural environment.[5] Legionella species are the causative agent of the human Legionnaires' disease and the lesser form, Pontiac fever. Legionella transmission is via aerosols—the inhalation of mist droplets containing the bacteria. Common sources include cooling towers, domestic hot-water systems, fountains, and similar disseminators that tap into a public water supply. Natural sources of Legionella include freshwater ponds and creeks. Person-to-person transmission of Legionella has not been demonstrated.[6]

Once inside a host, incubation may take up to two weeks. Initial symptoms are flu-like, including fever, chills, and dry cough. Advanced stages of the disease cause problems with the gastrointestinal tract and the nervous system and lead to diarrhea and nausea. Other advanced symptoms of pneumonia may also present.

However, the disease is generally not a threat to most healthy individuals, and tends to lead to harmful symptoms only in those with a compromised immune system and the elderly. Consequently, it is actively checked for in the water systems of hospitals and nursing homes. In the United States, the disease affects between 8,000 to 18,000 individuals a year.

Controlling potential sources of Legionella

Common sources of Legionella include cooling towers used in industrial cooling water systems as well as in large central air conditioning systems, domestic hot water systems, fountains, and similar disseminators that draw upon a public water supply. Natural sources include freshwater ponds and creeks.

Recent research in the Journal of Infectious Diseases provides evidence that Legionella pneumophila, the causative agent of Legionnaires disease, can travel at least 6 km from its source by airborne spread. It was previously believed that transmission of the bacterium was restricted to much shorter distances. A team of French scientists reviewed the details of an epidemic of Legionnaires disease that took place in Pas-de-Calais in northern France in 2003–2004. There were 86 confirmed cases during the outbreak, of whom 18 perished. The source of infection was identified as a cooling tower in a petrochemical plant, and an analysis of those affected in the outbreak revealed that some infected people lived as far as 6–7 km from the plant.[7]

Several European countries established a working group known as the European Working Group for Legionella Infections (EWGLI)[8] to share knowledge and experience about monitoring potential sources of Legionella. That group has published guidelines about the actions to be taken to limit the number of colony forming units (i.e. live bacteria that are able to multiply) of Legionella per litre

Legionella bacteria cfu/litreAction required - 35 samples per facility is required, 20 water / 10 swabs
1000 or lessSystem under control. (150+ CFU/ml in healthcare facilities or nursing homes require immediate action)
more than 1000
up to 10,000
Review program operation. The count should be confirmed by immediate re-sampling. If a similar count is found again, a review of the control measures and risk assessment should be carried out to identify any remedial actions.
more than 10,000Implement corrective action. The system should immediately be re-sampled. It should then be ‘shot dosed’ with an appropriate biocide, as a precaution. The risk assessment and control measures should be reviewed to identify remedial actions.

Temperature affects the survival of Legionellae as follows:

  • 70 to 80 °C (158 to 176 °F) - Disinfection range
  • At 66 °C (151 °F) - Legionellae die within 2 minutes
  • At 60 °C (140 °F) - Legionellae die within 32 minutes
  • At 55 °C (131 °F) - Legionellae die within 5 to 6 hours
  • 50 to 55 °C (122 to 131 °F) - They can survive but do not multiply
  • 20 to 50 °C (68 to 122 °F)- Legionellae growth range
  • 35 to 46 °C (95 to 115 °F) - Ideal growth range
  • Below 20 °C (68 °F) - Legionellae can survive but are dormant

The above data can be confirmed in an online article by Reliance World Wide.[9]

Control of Legionella growth can be through :

 A. Chemical Treatment
    1. Short term - Cl2, must be repeated every 3 to 5 weeks, corrosion factors
    2. Long term - ClO2, takes up to 17 months for system saturation
 B. Non-Chemical Treatment
    1. Short term - Thermal eradication - must be repeated every 3 to 5 weeks
    2. Long term - Industrial size copper silver ionisation (Ionization) technology such as, 2-Liquitech or 3-TarnPure.

Guidelines for control of Legionella in cooling towers

Many governmental agencies, cooling tower manufacturers and industrial trade organizations have developed design and maintenance guidelines for preventing or controlling the growth of Legionella in cooling towers. Below is a list of sources for such guidelines:

  • [
  • [1] ASHRAE Guideline
  • Centers for Disease Control and Prevention - Procedure for Cleaning Cooling Towers and Related Equipment (pages 239 and 240 of 249)
  • Cooling Technology Institute - Best Practices for Control of Legionella
  • Association of Water Technologies - Legionella 2003
  • California Energy Commission - Cooling Water Management Program Guidelines For Wet and Hybrid Cooling Towers at Power Plants
  • Marley Cooling Technologies - Cooling Towers Maintenance Procedures
  • Marley Cooling Technologies - ASHRAE Guideline 12-2000 - Minimizing the Risk of Legionellosis
  • Marley Cooling Technologies - Cooling Tower Inspection Tips {especially page 3 of 7}
  • [2] - TEC: Cooling tower company with all certificates needed for handling legionalla
  • Tower Tech Modular Cooling Towers - Legionella Control
  • GE Infrastructure Water & Process Technologies - Chemical Water Treatment Recommendations For Reduction of Risks Associated with Legionella in Open Recirculating Cooling Water Systems


  1. ^ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th Edition, McGraw Hill. ISBN 0-8385-8529-9. 
  2. ^ ISO 11731
  3. ^
  4. ^
  5. ^ Swanson M, Hammer B (2000). "Legionella pneumophila pathogesesis: a fateful journey from amoebae to macrophages". Annu Rev Microbiol 54: 567-613. PMID 11018138.
  6. ^ Winn, W.C. Jr. (1996). Legionella (In: Baron's Medical Microbiology, Baron, S. et al, eds., 4th Edition, University of Texas Medical Branch. ISBN 0-9631172-1-1.  (via NCBI Bookshelf)
  7. ^ Nguyen T, Ilef D, Jarraud S, Rouil L, Campese C, Che D, Haeghebaert S, Ganiayre F, Marcel F, Etienne J, Desenclos J (2006). "A community-wide outbreak of legionnaires disease linked to industrial cooling towers--how far can contaminated aerosols spread?". J Infect Dis 193 (1): 102-11. PMID 16323138.
  8. ^ European Working Group for Legionella Infections
  9. ^ What is Legionnaires' Disease?

See also

  • Images of Legionella bacteria:
  • Images
  • Support groups:
  • The world's only English support Group
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Legionella". A list of authors is available in Wikipedia.
Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE