Legionella pneumophila (Legionnaires disease and Pontiac fever)
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Legionella pneumophila (Legionnaires disease and Pontiac fever)
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Legionella pneumophila (Legionnaires disease and Pontiac fever)
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| Laboratory value | Result |
| Serum chemistries | |
| Hemoglobin | 12.6 g/dL |
| Hematocrit | 39 % |
| Leukocyte count | 19,000/mm3 |
| Platelet count | 50,000/mm3 |
| Sodium | 130 mEq/L |
| Potassium | 4.2 mEq/L |
| Chloride | 97 mEq/L |
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Legionella pneumophila p. , 124, 141
Legionella pneumophila p. , 141
Macrolides p. 190
Legionella pneumophila p. , 141
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Content Reviewers
Rishi Desai, MD, MPHContributors
Alexandru Duhaniuc, MD
Legionella pneumophila is a Gram-negative bacillus, which means is shaped like a rod, and can be found in many water systems, such as hot water tanks, cooling towers, large air conditioning systems or hot tubs.
It is typically transmitted by inhaling infected aerosols, like contaminated water sprays, jets, or mists and causes a disease called legionellosis with two distinct entities.
The first one, Legionnaires’ disease got its name from a deadly outbreak of pneumonia in 1976 among people attending a convention of the American Legion, and the second one, Pontiac fever, got its name from Pontiac, Michigan, where the first case was recognized.
Now, Legionella pneumophila has a very thin peptidoglycan layer, so it stains like a Gram-negative bacteria.
But it stains pretty weakly as a Gram-negative bacteria, so it’s best visualized with silver stain.
Legionella pneumophila is non-spore forming, aerobic, which means it needs oxygen to survive, facultative intracellular, which means it can survive both inside and outside the cell, and oxidase and catalase positive, which means it produces both of these enzymes.
Finally, it needs special nutrients to grow, such as cysteine and iron, so it grows on a special medium called buffered charcoal yeast extract, or BCYE, which contains cysteine and iron that are essentially for growth of Legionella.
So, on this medium, it forms grey-white colonies with a cut-glass appearance.
Now, Legionella pneumophila can enter the body through inhalation of contaminated water droplets.
Once it reaches the lungs, it gets ingested by alveolar macrophages and inside macrophages, it gets wrapped up in a vesicle called phagosome, which normally merges with lysosomes to kill invading bacteria.
However, Legionella has a type IVB secretion system, which uses effector proteins to prevent phagolysosomal fusion.
As a result, Legionella is able to survive and replicate inside macrophages.
Summary
Legionella pneumophila is a Gram-negative rod-shaped bacteria that can be found in many water systems, such as hot water tanks, cooling towers, large air conditioning systems, or hot tubs. It is typically transmitted by inhaling infected aerosols, like contaminated water sprays, jets, or mists, and causes a disease called legionellosis with two distinct forms.
First, there is Legionnaires' disease which causes severe pneumonia with high-grade fever. It can also cause some gastrointestinal symptoms such as vomiting and diarrhea and neurological symptoms such as headache and confusion. The second form is Pontiac fever, which is a much milder disease without pneumonia, but with some flu-like symptoms.
Legionella pneumophila is diagnosed by identifying Legionella in a culture from respiratory tract secretions and using a urinary antigen test. Legionnaires' disease is treated with macrolides and fluoroquinolone antibiotics, whereas Pontiac fever may resolve spontaneously.
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