LEGIONELLA PNEUMOPHILA: CHARACTERISTICS, MORPHOLOGY, PATHOLOGY - BIOLOGY - 2025

Phylum: Proteobacteria

Class: Gamma Proteobacteria

Order: Legionellales

Family: Legionellaceae

Genus: Legionella

Species: pneumophila

Pathogeny

The generally immunosuppressed patient acquires the bacteria by inhaling it in aerosols generated by air conditioning systems, shower heads, heating systems, nebulizers, among others.

Legionella pneumophila is a facultative intracellular pathogen. Upon reaching the lung, it is phagocytosed by alveolar macrophages, adhering to it through pili and outer membrane proteins (OMP).

On the other hand, the C3 component of complement is deposited on the bacterium and uses the CR1 and CR3 receptors of phagocytic cells to adhere.

Another membrane protein called MIP (macrophage invasion enhancer) also participates in the adhesion process. Once the macrophage is invaded, it stops the process of destroying the microorganism and instead the bacterium takes control of it to reproduce.

Finally the macrophage smooths out and releases the bacteria that will infect other macrophages and mononuclear cells.

Pathology

The incubation period is 2 to 10 days.

Legionella pneumophila in addition to legionellosis can cause a variant of the disease called Pontiac fever, as well as it can affect extrapulmonary anatomical areas.

Legionellosis or Legionnaires' disease

It is characterized by presenting as a picture of necrotizing pneumonia with multiple foci. It starts with a feeling of discomfort that progresses over time, mild headache, muscle aches.

The first day there may be a high fever (38.8 - 40 ° C or higher), chills, and a dry cough at first that can later become productive.

Some patients may have gastrointestinal symptoms such as abdominal pain, nausea, vomiting, and diarrhea. At the pulmonary level, pneumonia, pleural effusion and in some cases lung abscesses are observed.

The chest radiograph may reveal initial sectoral infiltrates that can progress to consolidation of all five lung lobes. Infiltrates occur in both lungs in most cases, and abscess cavities can be seen.

Extrapulmonary lesions may also occur, including renal failure with proteinuria, azotemia, and hematuria. Likewise, moderate alterations in liver function can be seen.

At the central nervous system level, drowsiness, delusions, disorientation, confusion, drowsiness, and seizures are rarely observed.

The manifestations on the skin are extremely rare, but when it occurs it is a macular rash, not pruritic and painful at the level of the legs.

The mortality rate is 15-30%.

Pontiac fever

Pontiac fever is a benign, self-limited disease. The incubation period is 1 to 2 days.

Symptoms are similar to a common flu, with fever, chills, and myalgia, there may be a cough, chest or pleuritic pain, and confusion.

There are no manifestations that show involvement of other organs. The mortality rate for this pathology is 0%

Diagnosis

Legionella pneumophila does not grow on blood agar, nor on any other medium used for common respiratory pathogens.

Therefore, for its isolation a special medium agar-yeast extract-buffered activated carbon (BCYEa) is used at a pH of 6.9, which contains the substances required by this microorganism.

The culture medium can be supplemented with antibiotics to make the medium selective for Legionella, as other bacteria are capable of growing on this medium such as Francisella tularensis, Bordetella pertussis, and spore-forming bacilli.

Colonies grow slowly, with growth observed after 3 days of incubation at 35 ° C and 90% humidity. In blood cultures it can take up to 2 or more weeks to grow.

To identify community outbreaks, isolates isolated from patients should be compared with strains isolated from the suspected environment as a source of contamination.

One of the techniques used to compare clinical and environmental strains is Pulsed-Field Gel Electrophoresis (PFGE, pulsed field electrophoresis).

Treatment

Antibiotics that can enter cells should be used. The best options are: fluoroquinolones, macrolides, and rifampin.

Usually one tablet of levofloxacin 750 mg is indicated, for seven to ten days. In transplant patients, this drug is used for up to 21 days. Another alternative is parenterally.

It can also be treated with azithromycin, 1 g the first day followed by 500 mg once a day for seven to 10 days.

Prevention

Sterile water should be used for washing, rinsing and refilling healthcare devices and refrigeration systems.

Disinfection with ultraviolet light is recommended, as with ionization of copper and silver. Chlorinating water is not effective against Legionella pneumophila, but is inactivated by heating the water above 70 ° C.

References

1. Ragull S, García-Núñez M, Pedro-Botet M, Rey-Joly C, Sabria M. Diversity of Legionella pneumophila subtypes in cooling towers: growth kinetics and virulence studies. Rev Infectious Diseases and Clinical Microbiology, 2011; 9 (5): 325-402
2. Brady MF, Sundareshan V. Legionnaires' Disease (Legionella Infection). In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2018 Jan-. Available from: ncbi.nlm.nih.gov
3. David S, Afshar B, Mentasti M, et al. Seeding and Establishment of Legionella pneumophila in Hospitals: Implications for Genomic Investigations of Nosocomial Legionnaires' Disease. Clin Infect Dis. 2017; 64 (9): 1251-1259.
4. Legionella pneumophila. Biological agents file. National Institute of safety and hygiene at work. Databio. 2012; DB-BL.p-12. Available at: insht.es
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9. Wikipedia contributors. Legionella pneumophila. Wikipedia, The Free Encyclopedia. August 15, 2018, 19:17 UTC. Available at: wikipedia.org.