Legionella and bacterial pneumonia
One of the major culprits of bacterial pneumonia is legionella, a non-fermenting gram-negative aerobic bacterium obliged: legionella - in particular the pneumophila species - is called an environmental killer in all respects.
Historical events
The name "legionella", particular and bizarre, originates from a famous conference of legionaries, former combatants of the Vietnam war, held at the Bellevue-Stratforf Hotel in Philadelphia in the summer of 1976: in that year, 221 Legionnaires - among the 4, 000 present - they were struck by a strange lung inflammation and, for 34 of these, the outcome was fatal. At first glance, the Russians were accused of the hypothetical biological attack, but the following year they discovered the real reasons that caused the disease: in the hotel ventilation system, a new beating was identified, later called Legionella pneumophila precisely in memory of the tragic event.
Microbiological description
Legionella is the only genus belonging to the Legionellaceae family; the bacteria are intracellular, gram-negative, obligatory and asporigenic parasites, presenting one or two lateral and polar flagella. Legionella has variable dimensions, from 0.3 to 0.9 µm in width and from 1.5 to 5 µm in length [taken from www.legionellaonline.it]
To date, over 40 species of Legionella have been identified, of which pneumophila is certainly the most dangerous, responsible for over 90% of cases of bacterial pneumonia.
Legionella is defined as an inert bacteria: this means that they are not fermentants (fermentative activity of sugars almost nothing / scarce). Biochemical tests have shown a certain positivity of legionella in catalase, beta-lactamase, gelatinase, hippurate hydrolysis and mobility tests, as well as a negativity in urease and nitrate tests.
Biochemical characters
Legionella bacteria feed on amino acids such as arginine, cysteine, methionine and isoleucine; their development is stimulated by iron and its derivatives.
In the laboratory, they develop in special cultivation soils, clearly rich in amino acids, iron salts and yeasts, very useful - as well as indispensable - elements for their development.
Diffusion and habitat
The environment represents the natural reservoir of legionellae: strictly speaking, it is understandable that these bacteria are particularly widespread in nature, in particular near natural aquatic environments (lakes, rivers, ponds, marine environments) and in wet soils. Even artificial aquatic places (eg fountains, pipes, pools, etc.) can be an ideal habitat for the replication of legionellae.
As can be seen from the tragic event of 1976, legionellae replicate also in the hot-humid sections of the ventilation systems (air conditioners, air humidifiers, etc.).
Some ciliate protozoa and amoebas are sometimes a source of nutrition - therefore a reservoir - of legionella.
Legionellae replicate at pHs ranging from 5.4 to 8.1; furthermore, these bacteria maintain their replication capacity unchanged over a very wide range of temperatures (5.7-55 ° C), despite the ideal thermal replication condition being around 25-42 ° C.
Transmission of the bacterium
Currently, in our country, legionella infections are related to the pollution of water distribution plants. The beat is transmitted by inhalation of infected water droplets and, only rarely, the infection occurs through microparticles of dust deriving from the drying of contaminated aerosols: in other words, all the places where it is possible to contact with atomized water are possible sources of contagion.
The transmission between man and man is unlikely.
Fortunately, despite the many places of contagion - both natural and artificial - there are very few diseases caused by legionella: populations living near contaminated areas only rarely contract the disease.
However, the self-protection mechanisms triggered in the body still remain the object of study.
Related diseases
In general, diseases caused by legionella are known as legionellosis. However, a distinction is appropriate: there are two directly related infections, Legionnaires' disease and Pontiac fever.
Legionnaires' disease - to which an entire in-depth article will be dedicated - represents the most severe form of legionellosis, with a poor prognosis of 10 to 50%: so much so that often the aforementioned disease is understood as legionellosis. It is an acute pneumonia that begins with the typical symptoms of influenza: in this regard, it is often misdiagnosed, therefore not recognized promptly.
Pontiac fever is a mild form of legionellosis that does not affect the lung and presents itself as an acute self-limiting disease. In this case, legionella infection can occur even without any symptoms and remain unnoticed.
