Legionella

Taxobox
color = lightgrey
name = "Legionella"

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image_width = 240px
image_caption = "Legionella sp." under UV illumination.
domain = Bacteria
phylum = Proteobacteria
classis = Gamma Proteobacteria
ordo = Legionellales
familia = Legionellaceae
genus = "Legionella"
genus_authority = Brenner "et al." 1979
subdivision_ranks = Species
subdivision = "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". [cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th Edition | publisher = McGraw Hill | year = 2004 | id = ISBN 0-8385-8529-9 ] cite book | author = Heuner K, Swanson M (editors). | title = Legionella: Molecular Microbiology | publisher = Caister Academic Press | year = 2008 | url=http://www.horizonpress.com/leg | id = [http://www.horizonpress.com/leg ISBN 978-1-904455-26-4 ] ]

"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 acquired its name after a July, 1976 outbreak among people attending a convention of the American Legion in Philadelphia. The mystery disease sickened 221 persons, causing 34 deaths. In that bicentennial year, a pandemic among U.S. war veterans was widely publicized and produced a national panic [cite web|author=Lawrence K. Altman |title=In Philadelphia 30 Years Ago, an Eruption of Illness and Fear|date=09-01-2006|publisher=New York Times|url=http://www.nytimes.com/2006/08/01/health/01docs.html?_r=1&oref=slogin&pagewanted=print] .On January 18, 1977 the causative agent was identified as a previously unknown bacterium, subsequently named Legionella. See Legionnaire's Disease for full details.

Detection

"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 [ISO 11731] concentrate the bacteria (by centrifugation and/or filtration through 0.2 micrometre filters) before inoculation 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 interference 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) [ [http://www.genesystems.fr/ Biologie moléculaire, diagnostic moléculaire, microbiologie, biotechnologies ] ] and rapid immunological assays [ [http://www.hydrosense.biz/hydrosense/default.asp?p=44 Legionella Field Test - Products - Hydrosense ] ] . These technologies can typically provide much faster results.

Pathogenesis

"Legionella" have been known for some time to live within amoebae in the natural environment.cite journal |author=Swanson M, Hammer B |title=Legionella pneumophila pathogesesis: a fateful journey from amoebae to macrophages |journal=Annu Rev Microbiol |volume=54 |pages=567–613 |year=2000 |pmid=11018138 |doi=10.1146/annurev.micro.54.1.567] "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. [cite book | author = Winn, W.C. Jr. | title = Legionella (In: Baron's Medical Microbiology, Baron, S. et al, eds.| edition = 4th Edition | publisher = University of Texas Medical Branch | year = 1996 | id = ISBN 0-9631172-1-1 [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.2229 (via NCBI Bookshelf)] ]

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.

Molecular biology

With the application of modern molecular genetic and cell biological techniques, the mechanisms used by "Legionella" to multiply within macrophages are beginning to be understood. The specific regulatory cascades that govern differentiation as well as the gene regulation are being studied. The genome sequences of four "L. pneumophila" strains have been published and it is now possible to investigate the whole genome by modern molecular methods. The molecular studies are contributing to the fields of clinical research, diagnosis, treatment, epidemiology, and prevention of disease.cite book | author = Heuner K, Swanson M (editors). | title = Legionella: Molecular Microbiology | publisher = Caister Academic Press | year = 2008 | url=http://www.horizonpress.com/leg | id = [http://www.horizonpress.com/leg ISBN 978-1-904455-26-4 ] ]

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.cite journal |author=Nguyen T, Ilef D, Jarraud S, Rouil L, Campese C, Che D, Haeghebaert S, Ganiayre F, Marcel F, Etienne J, Desenclos J |title=A community-wide outbreak of legionnaires disease linked to industrial cooling towers--how far can contaminated aerosols spread? |journal=J Infect Dis |volume=193 |issue=1 |pages=102–11 |year=2006 |pmid=16323138 |doi=10.1086/498575]

Several European countries established a working group known as the European Working Group for Legionella Infections (EWGLI) [ [http://www.ewgli.org European Working Group for Legionella Infections] ] 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

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. [ [http://www.relianceworldwide.com/site/fs_legionella.htm What is Legionnaires' Disease?] ]

Control of "Legionella" growth can be through :A. Chemical Treatment:#Short term - Cl2, must be repeated every 3 to 5 weeks, corrosion factors:#Long term - ClO2, takes up to 17 months for system saturationB. Non-Chemical Treatment:#Short term - Thermal eradication - must be repeated every 3 to 5 weeks:#Long term - Industrial size copper silver ionisation (Ionization)

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:
* [http://www.legionella.org
* [http://www.ashrae.org/publications/detail/14891#Gdl12] ASHRAE Guideline
* [http://www.cdc.gov/ncidod/dhqp/pdf/guidelines/Enviro_guide_03.pdf Centers for Disease Control and Prevention] - Procedure for Cleaning Cooling Towers and Related Equipment (pages 239 and 240 of 249)
* [http://www.cti.org/downloads/legion_2000.pdf Cooling Technology Institute] - Best Practices for Control of Legionella
* [http://www.awt.org/IndustryResources/Legionella03.pdf Association of Water Technologies] - Legionella 2003
* [http://www.energy.ca.gov/2005publications/CEC-700-2005-025/CEC-700-2005-025.PDF California Energy Commission] - Cooling Water Management Program Guidelines For Wet and Hybrid Cooling Towers at Power Plants
* [http://www.thermalenergy.co.uk] - TEC: Cooling tower company with all certificates needed for handling legionalla
* [http://www.towertechinc.com/documents/Legionella_Control_White_Paper_05072004.pdf Tower Tech Modular Cooling Towers] - Legionella Control
* [http://www.gewater.com/pdf/tech73.pdf GE Infrastructure Water & Process Technologies ] - Chemical Water Treatment Recommendations For Reduction of Risks Associated with Legionella in Open Recirculating Cooling Water Systems
* [http://www.procareh2o.com/pdf/aqualyse_08_usa.pdf Facility Legionella Control Technology ] - Hotel, Healthcare and Nursing Home Water Treatment Recommendations For Reduction of Risks Associated with Legionella bacterium in Potable Water Networks

References

ee also

* "Legionella pneumophila"
* Biocide
* Legionellosis
* European Working Group for Legionella Infections
* Environmental microbiology

External links

* [http://www.ashrae.org/publications/detail/14891#Gdl12/ ASHRAE Guideline]
* [http://www.cdc.gov/ncidod/dbmd/diseaseinfo/legionellosis_t.htm CDC Division of bacterial and Mycotic Diseases: Legionellosis]
* [http://www.astdhpphe.org/infect/legion.html Directors of Health Promotion and Education page on Legionellosis]
* [http://www.ewgli.org/ European Working Group for Legionella Infections]
* [http://www.q-net.net.au/~legion Legionnaires' disease Outbreaks]
* [http://www.hcinfo.com/outbreaks-news.htm Recent outbreaks of Legionnaires' Disease]
* [http://www.legionella.org The Legionella Experts]

Images of "Legionella" bacteria:
* http://newsimg.bbc.co.uk/media/images/38922000/jpg/_38922367_legionella203.jpg
* http://www.chemistryquestion.com/images/Question/legionella.jpg
* [http://www.q-net.net.au/~legion/Legionnaires_Disease_Bugs_Of_This_World.htm Images]