What is legionella ?

What is legionella ?

Legionella culture under UV –

Legionella belongs to the Legionellacea family, which includes 48 species. Half of these can infect human beings. They are microscopic bateria which can reach 2 micrometers in size. They are intracellulars, meaning that they live inside cells,but they have the ability to survive outside cells as well.


The Legionella species grow in aquatic environments where optimal temperatures range for 20°C ± 1°C to 45°C ±1°C. Beyond 70°C± 1°C, no more development is possible.

Source Amara et al., 2016

Legionella spp. develop especially well in high-temperature water sources .

They are present, in natural low-salinity environments such as lakes, rivers or groundwater .  Their growth is facilitated by microbial interactions as well as the presence of certains metallics minerals, including iron and zinc. Stagnant water and also favors these developements. When biofilm are formed it allow protection and resistance for bacteria and the colonisation is easier.

Man-made water systems are not legionella safe. In fact, they can proliferate many differents environments. Thus, aerosols or water storage sources are ideal locations for waterborne pathogens growth. Examples include air humidifiers, water heaters, cooling towers, and air conditioning units.

Waterborne pathogens proliferate in water droplets inside human respiratory tract. This, leads to a human pathology , called “Legionnaires’ disease” caused specifically by Legionella pneumophila. Its symptoms range from fever and diarrhea to full-on pneumonia.

Nevertheless, it’s important to note that according to various scientific studies on Legionnaire’s disease, around 15% of cases were fatal.


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