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{{Legionellosis}}
{{Taxobox
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| binomial_authority = Brenner DJ, Steigerwalt AG, McDade JE 1979
| binomial_authority = Brenner DJ, Steigerwalt AG, McDade JE 1979
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{{About0|Legionellosis}}
{{For|information on other species in Legionella|Legionella}}
 
{{CMG}}
{{CMG}}


==Overview==
==Overview==
'''''Legionella pneumophila''''' is a thin, [[Wiktionary:pleomorphism|pleomorphic]], [[flagella]]ted
''L.pneumophila'' is a ubiquitous aquatic organism that thrives in warm environments (32°- 45°C). ''L. pneumophila'' is a [[pleomorphic]], [[aerobic]], [[catalase]]-positive, [[oxidase]]-positive, [[Endospore|non-spore-forming]], non-capsulated, [[motile]], Gram-negative bacteria. Although ''[[Legionella]]'' is categorized as a [[Gram-negative bacteria|Gram-negative bacterium]], it stains poorly to Gram stain due to its unique [[lipopolysaccharide]]-content in the outer psuedospamodulating leaflet of the outer cell membrane.
[[Gram-negative]] bacterium of the genus ''[[Legionella]]''.<ref name=Brock>{{cite book | author = Madigan M; Martinko J (editors). | title = Brock Biology of Microorganisms | edition = 11th ed. | publisher = Prentice Hall | year = 2005 | id = ISBN 0-13-144329-1 }}</ref> ''L. pneumophila'' is the primary human [[pathogen]] in this group and is the causative agent of [[legionellosis]] or [[Legionnaires' disease]].
 
==Microbiological Classification==
*[[Bacteria]]; [[Proteobacteria]]; [[Gammaproteobacteria]]; [[Legionellales]]; [[Legionellaceae]]


==Characterization==
==Microbiological Characteristics==
''L. pneumophila'' is non-[[acid-fast]], non-[[Endospore|sporulating]], endochronogimalational and morphologically a non-capsulated rod-like bacteria.  [[Aerobic]] and unable to [[hydrolysis|hydrolyse]] [[gelatin]] or produce [[urease]], they are also non-[[Fermentation (biochemistry)|fermentative]]. ''L. pneumophila'' is neither [[pigment]]ed nor does it [[autofluorescence|autofluoresce]]. It is [[oxidase]]- and [[catalase]]-positive, and produces [[beta-lactamase]].  
*''L.pneumophila'' is a ubiquitous aquatic organism that thrives in warm environments (32°- 45°C).
*''L. pneumophila'' is a pleomorphic, [[aerobic]], [[catalase]]-positive, [[oxidase]]-positive, [[Endospore|non-spore-forming]], non-capsulated, [[motile]], [[Gram-negative bacteria]].
*Although ''Legionella'' is categorized as a [[Gram-negative bacteria|Gram-negative bacterium]], it stains poorly to Gram stain due to its unique [[lipopolysaccharide]]-content in the outer psuedospamodulating leaflet of the outer cell membrane.<ref name="Sherris">{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0-8385-8529-9 }}</ref>
*''[[Legionella]]'' is non-fermentative and is unable to [[hydrolysis|hydrolyse]] [[gelatin]] or produce [[urease]].
*At least 46 species and 70 serogroups of ''[[Legionella]]'' have been identified.
Legionella grow on buffered charcoal yeast enriched with L-cysteine <ref name="pmid16751507">{{cite journal| author=Ewann F, Hoffman PS| title=Cysteine metabolism in Legionella pneumophila: characterization of an L-cystine-utilizing mutant. | journal=Appl Environ Microbiol | year= 2006 | volume= 72 | issue= 6 | pages= 3993-4000 | pmid=16751507 | doi=10.1128/AEM.00684-06 | pmc=1489648 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=16751507  }} </ref>
*The natural habitat of Legionella is freshwater, where they often live within protozoa such as Vermamoeba vermiformis, Acanthamoeba spp., Tetrahymena pyriformis, and Naegleria spp <ref name="pmid11018138">{{cite journal| author=Swanson MS, Hammer BK| title=Legionella pneumophila pathogesesis: a fateful journey from amoebae to macrophages. | journal=Annu Rev Microbiol | year= 2000 | volume= 54 | issue=  | pages= 567-613 | pmid=11018138 | doi=10.1146/annurev.micro.54.1.567 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11018138  }} </ref>. It utilizes a similar method to enter and infect phagocytes <ref name="pmid11018138">{{cite journal| author=Swanson MS, Hammer BK| title=Legionella pneumophila pathogesesis: a fateful journey from amoebae to macrophages. | journal=Annu Rev Microbiol | year= 2000 | volume= 54 | issue=  | pages= 567-613 | pmid=11018138 | doi=10.1146/annurev.micro.54.1.567 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11018138  }} </ref>.                                                                                        


===Cell membrane structure===
==Life Cycle==
While ''L. pneumophila'' is categorized as a Gram-negative organism, it stains poorly due to its unique [[lipopolysaccharide]]-content in the outer psuedospamodulating leaflet of the outer cell membrane.<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0-8385-8529-9 }}</ref> On the side-chains of the cell wall are carried the bases 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 important means of serologically classifying many Gram-negative bacteria. At least 35 different [[serovar]]s of ''L. pneumophila'' have been described as well as several other species being subdivided into a number of serovars.
*One of the unique characteristics of Legionella pneumophila is that is has the ability to thrive within a large variety of hosts <ref name="pmid29404281">{{cite journal| author=Oliva G, Sahr T, Buchrieser C| title=The Life Cycle of L. pneumophila: Cellular Differentiation Is Linked to Virulence and Metabolism. | journal=Front Cell Infect Microbiol | year= 2018 | volume= 8 | issue= | pages= 3 | pmid=29404281 | doi=10.3389/fcimb.2018.00003 | pmc=5780407 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=29404281  }} </ref>.
*There are two major phases to the life cycle.
:*The first is called the replicative phase. During this period, the [[bacteria]] are nonmotile and have a low infectivity.
:*In the second phase, called the infectious phase, the bacteria are shorter and thicker.


[[Sera]] have been used both for slide agglutination studies as well as for direct detection of bacteria in tissues using [[fluorescence|fluorescent]]-labelled [[antibody]]. Specific antibody in patients can be determined by the indirect fluorescent antibody test. [[ELISA]] and microagglutination tests have also been successfully applied.
==Gallery==
[[File:Legionella microscopy.jpg|thumb|none|Colorized scanning electron micrograph (SEM) depicted a large grouping of Gram-negative Legionella pneumophila bacteria under 8000x magnification.<sup>Courtesy of Janice Haney Carr, Public Health Image Library<ref name="PHIL1">{{cite web |url=http://phil.cdc.gov/phil/details.asp |title=Public Health Image Library |last1=Haney Carr |first1=Janice |website= www.cdc.gov |access-date= Jan 15 2016}}</ref></sup>]]


==Pathogenesis==
[[File:Legionella microscopy 2.jpg|thumb|none|Colorized scanning electron micrograph (SEM) depicted a large grouping of Gram-negative Legionella pneumophila bacteria under 10,000x magnification.<sup>Courtesy of Janice Haney Carr, Public Health Image Library<ref name="PHIL2">{{cite web |url=http://phil.cdc.gov/phil/details.asp |title=Public Health Image Library |last1=Haney Carr |first1=Janice |website= www.cdc.gov |access-date= Jan 15 2016}}</ref></sup>]]
''L. pneumophila'' is a [[Wiktionary:facultative|facultative]] intracellular parasite that can invade and replicate inside [[amoebae]] and, in humans, in [[macrophage]]s. The internalisation of the bacteria can be enhanced by the presence of [[antibody]] and [[Complement system|complement]] but is not absolutely required. A [[pseudopod]] coils around the bacterium in this unique form of [[phagocytosis]]. Once internalised, the bacteria surround themselves in a membrane-bound vacuole that does not fuse with lysosomes that would otherwise degrade the bacteria. In this protected compartment the bacteria multiply. The bacteria use a Type IVB Secretion System known as Icm/Dot to inject effector proteins into the host. These effectors are involved in increasing the bacteria's ability to survive inside the host cell. They also secrete a 39kDa [[metalloprotease]] into culture fluids, which is [[cytotoxic]] for some cultured tissue culture cells.


The [[pathogen]]ic nature of ''L. pneumophila'' was first recognized after a 1976 outbreak among a group of elderly men attending an [[American Legion]] convention in [[Philadelphia, Pennsylvania]] (hence the name [[Legionellosis|Legionaires' disease]]). This outbreak affected over 200 individuals, with 34 fatalities. It is worth noting that person-to-person transmission of ''L. pneumophila'' has not been demonstrated.<ref name=Baron>{{cite book | author =  Winn WC Jr  | title = Legionella. ''In:'' Baron's Medical Microbiology ''(Baron S ''et al'', eds.)| edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | id = [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.2229 (via NCBI Bookshelf)] ISBN 0-9631172-1-1 }}</ref>
[[File:Pittsburgh pneumonia Legionella micdadei.jpg|thumb|none|Legionella micdadei bacteria using TATLOCK conjugate in egg yolk sac suspension, DFA-stained photomicrograph with positive HEBA stain.<sup>Courtesy of Ann Herbert, Public Health Image Library<ref name="PHIL3">{{cite web |url=http://phil.cdc.gov/phil/details.asp |title=Public Health Image Library |last1=Herbert |first1=Anne |website= www.cdc.gov |access-date= Jan 15 2016}}</ref></sup>]]
===Antimicrobial regimen===
:* 1.'''Atypical pneumonia (Legionnaires' disease )'''<ref>{{cite book | last = Bennett | first = John | title = Mandell, Douglas, and Bennett's principles and practice of infectious diseases | publisher = Elsevier/Saunders | location = Philadelphia, PA | year = 2015 | isbn = 978-1455748013 }}</ref>
::* 1.1  '''Mild pneumonia inpatient or outpatient, non immunocompromised'''
:::* Preferred regimen (1): [[Azithromycin]] 500 mg PO qd for 3-5 days
:::* Preferred regimen (2): [[Levofloxacin]] 500 mg PO qd for 7-10 days
:::* Preferred regimen (3): [[Ciprofloxacin]] 500 mg PO bid for 7-10 days
:::* Preferred regimen (4): [[Moxifloxacin]] 400 mg PO qd for 7-10 days
:::* Preferred regimen (5): [[Clarithromycin]] 500 mg PO bid for 10-14 days
:::* Alternative regimen (1): [[Doxycycline]] 200 mg PO loading dose, then 100 mg PO bid for 10-14 days
:::* Alternative regimen (2): [[Erythromycin]] 500 mg PO qid for 10-14 days
:::* Note: Patients with mild disease may be treated entirely with oral therapy
::* 1.2 '''Moderate to severe pneumonia or immunocompromised'''
:::* Preferred regimen (1): [[Azithromycin]] 500 mg PO/IV  q24h for 5-7 days
:::* Preferred regimen (2): [[Levofloxacin]] 500 mg PO/IV q24h for 7-10 days {{or}} 750 mg PO/IV q24h for 5-7 days
:::* Alternative regimen (1): [[Ciprofloxacin]] 750 mg PO bid for 14 days 
:::* Alternative regimen (2): [[Moxifloxacin]] 400 mg PO qd for 14 days
:::* Alternative regimen (3): [[Erythromycin]] 750-1000 mg IV q6h for 3-7 days, then 500 mg PO qid for a total course of 21 days
:::* Alternative regimen (4): [[Clarithromycin]] 500 mg IV q12h for 3-7 days, and then 500 mg PO bid  for a total course of 21 days
:::* Note: Severely ill patients parenteral therapy is advised until improvement is seen and oral absorption is sufficient.
:*  2 '''Pontiac fever'''
::*  Pontiac fever is febrile, self-limited form of Legionella infection which requires only symptomatic therapy, such as analgesics for headache. Antibiotics are not indicated.


==References==
==References==

Latest revision as of 05:13, 4 May 2022

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Legionella pneumophila
TEM image of L. pneumophila
TEM image of L. pneumophila
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gamma Proteobacteria
Order: Legionellales
Family: Legionellaceae
Genus: Legionella
Species: L. pneumophila
Binomial name
Legionella pneumophila
Brenner DJ, Steigerwalt AG, McDade JE 1979
This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Legionellosis.
For information on other species in Legionella, see Legionella.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

L.pneumophila is a ubiquitous aquatic organism that thrives in warm environments (32°- 45°C). L. pneumophila is a pleomorphic, aerobic, catalase-positive, oxidase-positive, non-spore-forming, non-capsulated, motile, Gram-negative bacteria. Although Legionella is categorized as a Gram-negative bacterium, it stains poorly to Gram stain due to its unique lipopolysaccharide-content in the outer psuedospamodulating leaflet of the outer cell membrane.

Microbiological Classification

Microbiological Characteristics

Legionella grow on buffered charcoal yeast enriched with L-cysteine [2]

  • The natural habitat of Legionella is freshwater, where they often live within protozoa such as Vermamoeba vermiformis, Acanthamoeba spp., Tetrahymena pyriformis, and Naegleria spp [3]. It utilizes a similar method to enter and infect phagocytes [3].

Life Cycle

  • One of the unique characteristics of Legionella pneumophila is that is has the ability to thrive within a large variety of hosts [4].
  • There are two major phases to the life cycle.
  • The first is called the replicative phase. During this period, the bacteria are nonmotile and have a low infectivity.
  • In the second phase, called the infectious phase, the bacteria are shorter and thicker.

Gallery

Colorized scanning electron micrograph (SEM) depicted a large grouping of Gram-negative Legionella pneumophila bacteria under 8000x magnification.Courtesy of Janice Haney Carr, Public Health Image Library[5]
Colorized scanning electron micrograph (SEM) depicted a large grouping of Gram-negative Legionella pneumophila bacteria under 10,000x magnification.Courtesy of Janice Haney Carr, Public Health Image Library[6]
Legionella micdadei bacteria using TATLOCK conjugate in egg yolk sac suspension, DFA-stained photomicrograph with positive HEBA stain.Courtesy of Ann Herbert, Public Health Image Library[7]

References

  1. ↑ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. ISBN 0-8385-8529-9.
  2. ↑ Ewann F, Hoffman PS (2006). "Cysteine metabolism in Legionella pneumophila: characterization of an L-cystine-utilizing mutant". Appl Environ Microbiol. 72 (6): 3993–4000. doi:10.1128/AEM.00684-06. PMC 1489648. PMID 16751507.
  3. ↑ 3.0 3.1 Swanson MS, Hammer BK (2000). "Legionella pneumophila pathogesesis: a fateful journey from amoebae to macrophages". Annu Rev Microbiol. 54: 567–613. doi:10.1146/annurev.micro.54.1.567. PMID 11018138.
  4. ↑ Oliva G, Sahr T, Buchrieser C (2018). "The Life Cycle of L. pneumophila: Cellular Differentiation Is Linked to Virulence and Metabolism". Front Cell Infect Microbiol. 8: 3. doi:10.3389/fcimb.2018.00003. PMC 5780407. PMID 29404281.
  5. ↑ Haney Carr, Janice. "Public Health Image Library". www.cdc.gov. Retrieved Jan 15 2016. Check date values in: |access-date= (help)
  6. ↑ Haney Carr, Janice. "Public Health Image Library". www.cdc.gov. Retrieved Jan 15 2016. Check date values in: |access-date= (help)
  7. ↑ Herbert, Anne. "Public Health Image Library". www.cdc.gov. Retrieved Jan 15 2016. Check date values in: |access-date= (help)
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