Legionella pneumophila: Difference between revisions

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

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Revision as of 16:23, 15 January 2016

This page is about microbiologic aspects of the organism(s). For clinical aspects of the disease, see Legionellosis.

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 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 Characteristics

L.pneumophila is a ubiquitous aquatic organism that thrives in warm environments (32°- 45°C).
L. pneumophila is 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.^[1]
Legionella is non-fermentative and is unable to hydrolyse gelatin or produce urease.
At least 46 species and 70 serogroups of Legionella have been identified.

Life Cycle

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 toxicity.
In the second phase, called the infectious phase, the bacteria are shorter and thicker.

References

↑ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. ISBN 0-8385-8529-9.

[Sherris-1] Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. ISBN 0-8385-8529-9.

[1]

@@ Line 23: / Line 23: @@
 ==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 pleomorphic, aerobic, catalase-positive, oxidase-positive, [[Endospore|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.
-[[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]].
-==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 pleomorphic, aerobic, catalase-positive, oxidase-positive, [[Endospore|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.<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.
-===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.
+*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 toxicity.
-[[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.
+:*In the second phase, called the infectious phase, the bacteria are shorter and thicker.
-==Pathogenesis==
-''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>
 ==References==