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MicroBioNet Your Microbiology Universe on the Internet |
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BACTERIOLOGY
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| Legionella pneumophila |
| CLASSIFICATION | VIRULENCE FACTORS | ENVIRONMENTAL |
| BIOCHEMISTRY | NORMAL FLORA | INDUSTRIAL USES |
| GENETICS | PATHOGENS | VACCINES |
| SEROLOGY | LABORATORY ID |
They are Gram-negative non-acid fast non-capsulated rods 0.3-0.9 µm x 2-20µm. They are aerobic and do not hydrolyse gelatin or produce urease. They are non-fermentative.
L. pneumophila is neither pigmented nor does it autofluoresce. It is oxidase and catalase positive, produces beta-lactamase. It is a strict aerobe. It hydrolyses hippurate and liquifies gelatin but does not ferment any carbohydrates. It requires specialised media for growth.
There is up 67% relatedness between the species on the basis of DNA hybridization studies.
DNA probes specific for
rRNA sequences of Legionella have been produced, as have ones for other
specific genes.
Plasmids have been
demonstrated in many species and plasmid profile analysis has been used to
characterise relationships between strains.
At least 14 different
serovars of L. pneumophila have been described as well as several
other species being subdivided into a number of serovars. Sera have been
used both for slide agglutination studies as well as for direct detection
of bacteria in tissues using 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.
L. pneumophila
is an intracellar pathogen. The internalisation of the bacteria is enhanced
by the presence of antibody and complement. A pseudopod coils around the
bacterium in this unique form of phagocytosis. Once Internalised, the bacteria
surround themselves by a membrane-bound phagolysosome. This becomes a vescicle,
within which the bacteria multiply.
They produce a
39kDa metalloprotease into culture fluids, which is cytotoxic for some cultured
tissue culture cells. This may be a virulence factor.
A novel cytotoxin
consisting of small peptides, which are acid and heat resistant has also
been described.
L. pneumophila
may also have a unique iron scavanging system.
Apart from carriers Legionallae do not form part of the normal flora of humans or animals.
Intestinal Infections:
These may only occur as
part of respiratory infections, where gastrointestinal symptoms have on occasion
been described.
Extraintestinal Infections:
L. pneumophila is specifically considered as a pathogen of the respiratory tract, where it is a cause of atypical pneumonia, also known as Legionnaires' disease.
Other infections have
also been reported, including haemodialysis fistulae, pericarditis and wound
and skin infections. Bacteraemia is often associated with Legionnaires' disease.
Animal Infections:
None specifically recorded.
Infections of Protozoa:
Protozoa such as Harmanella
vermiformis and related protozoa have been shown to be able to support
the growth of L. pneumophila in tap water. Also Acanthamoeba
, Naegleria and Tetrahymena can be infected by L. pneumophila
. It is considered that this may be how these fastidious organisms survive
in the environment.
The methods of choice
are cultivation of specimens on specific media and testing for the presence
of L. pneumophila colonies by their characteristic ground-glass appearance.
Otherwise direct fluorescent
staining, detection of specific antigen in blood or urine have been successfully
used.
Determination of a rise in antibody levels by indirect fluorescent antibody techniques is also a useful diagnostic tool.
They appear to occur ubiquitously in soils and particularly non-marine aqueous environments. They have been even found in pristine waters in tropical rain forests. Industrial water sources including airconditioning cooling towers and potable water systems have yielded L. pneumophila and been associated with outbreaks.
None are currently described.
None developed.
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GRAM
NEGATIVE
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FAMILIES
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| Acetobacteriaceae |
| Alcaligenaceae |
| Bacteroidaceae |
| Chromatiaceae |
| Enterobacteriaceae |
| Legionellaceae |
| Neisseriaceae |
| Nitrobacteriaceae |
| Pseudomonadaceae |
| Rhizobiaceae |
| Rickettsiaceae |
| Spirochaetaceae |
| Vibrionaceae |
| Genera of Unestablished Relationships |
| Brucella |
| Chromobacterium |
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