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Legionella pneumophila

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A non-capsulated aerobic and gram-negative single polar flagellum bacterium involved mostly in human Legionnaire’s disease.


Legionella pneumophila has a sized of about 2 micrometer in length and 0.3-0.9 micrometer in width surrounded by gram-negative cell wall and pili composed of branched chain fatty acid and ubiquinones. Its outer membrane contains lipopolysaccharide found to be pathophysiologic and less endotoxic due to the long chain fatty acids.

Legionella pneumophila is an aquatic bacterium that exists all over the globe as intracellular parasites of free living protozoa wherein particulate matter and natural microbial community promotes the growth of this bacterium especially inside hot water storage tank. It is also inhabits in constructed water system that prefers to grow in hot moist environment supplied by nutrients from sediments that formed interrelationships between temperature and microflora.

Legionella pneumophila has been identified as the main culprit behind Legionnaire’s disease that can only obtain from environmental source and never occurs between human-human interactions that cause bacterial pneumonia where it does not inhabit the upper respiratory tract due to its minute size which able to avoid the defenses of upper airways but grows intracellularly in the pulmonary alveolar macrophages.

Scientific classification:

Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gamma Proteobacteria
Family: Legionellaceae
Genus: Legionella
Species: Legionella pneumophila 

See also:


Legionnaire’s disease