Legionella Bacteria Testing

This bacterium has specific nutritional requirements in terms of iron and carbon sources necessary for its metabolism: it uses amino acids rather than sugars. The media on which it is cultivated are supplemented with amino acids to account for this particularity.

In connection with these requirements, the bacterium multiplies inside a host, namely macrophages** in the human lungs and free amoebae in the environment. These two types of cells use phagocytosis (internalisation of part of the external environment with the formation of a vesicle called a phagosome) to extract part of their food from the environment surrounding them. This is the preferred route by which L. pneumophila enters its host. At this stage, it begins to alter the internal functioning of the host, on the one hand by blocking the mechanisms that normally lead to the digestion of bacteria trapped in these phagosomes (digestive phagosomes) and, on the other hand, by stimulating intracellular protein degradation processes (to meet its amino acid requirements). It multiplies in this vesicle, which then takes the name replicative phagosome. Its growth is optimal at a temperature of 36ºC and remains significant in the range 25ºC – 42ºC. At a certain stage of development, the cell bursts, releasing a number of new bacteria that is still poorly documented.

L. pneumophila finds the most favourable conditions for multiplication in microbial biofilms that line all walls in contact with water, in the environment, and in human facilities. It is in this semi-confined environment that free amoebae proliferate and multiply.

** Amoeboid cells that move across the surface of the pulmonary alveoli, whose function is to rid them of particles of all kinds (including bacteria) that are brought there by respiration.

Legionnaires' disease is a severe form of pneumonia caused by infection of the lungs with L. pneumophila. In France, it affected nearly 2,000 people in 2019, with a fatality rate of around 10%. In its milder form, it presents with flu-like symptoms and is known as Pontiac fever.

There are currently around 15 known “variants” (serogroups) of the L. pneumophila species, some of which are more pathogenic than others (serogroups 1, 3, 4, and 6, in particular).

Other species of Legionella have been linked to respiratory diseases (L. anisa, for example).

The “legionella risk” to human health must be considered on two levels.

1 / That of emitting sites, sites where the proliferation of L. pneumophila is favoured, but also from which aerosols can be emitted. The most typical installations from this point of view are cooling towers, for three reasons:

• Their operating principle means that the water in the cooling circuit, present at a single point, has the conditions of warm water that are favourable to the development of biofilms and, more specifically, to that of amoebae and legionella.

• Cooling towers are subject to constant evaporation of water from the circuit and therefore to a concentration of its components (some of which are nutrients for bacteria), at least during part of their operating cycle.

• Cooling also relies on the evaporation of water by a ventilation system, which causes the emission of liquid and/or particulate aerosols.

2 / The second level of “legionella risk” is that of protecting individuals against the proliferation of legionella when it is unavoidable. The main points of the strategy by which individuals can be protected are as follows:

• The implementation of regular or opportunistic checks for the presence of L. pneumophila, which is covered by the service offered by ABIOLAB.

• The implementation of treatments for contaminated water (halogens, hydrogen peroxide, ozone, UV, and filtration devices).

• Raising user awareness of conditions that are conducive to water contamination, such as water stagnation in a water heater between two occupants of an apartment, or stagnation in shower heads.