Rapid Legionella Sampling


“Great communication at every step in the process”

“Great communication at every step in the process”

There are many different methods that exist to detect Legionella in domestic water systems.

The standard method for testing Legionella in water systems is the culture method which can take up to 10- 12 days to give a result. Timing is obviously crucial when you need the information to confirm that a water system is safe to use.

To meet this requirement, there are now a number of fast testing methods available on the market that provides an accurate Legionella result in less than 24 hours. The PCR (Polymerase Chain Reaction) test will detect the bacteria’s DNA and the LFICA (Lateral Flow Immunochromatographic Assay) will detect the presence of cell surface antigens from Legionella pneumophila.

It is important to note that different assays may give different results as they all use a different method of detection. A 100% correlation is unlikely but theLegipid®Legionella Rapid Test that Aqua Analyse offers is different from these tests and with respect to the laboratory test is more sensitive.

This is because the lab using culture methods need the bacterium to be in a productive stage to grow cultures, for positive results. There might be Legionella in the water that is Viable but Not Culturable not culturable (VNBC) due to it not being in the productive stage. It is quite possible therefore to test water for Legionella and get negative readings.

The Legipid® Legionella Fast Detection is a simple and rapid test for the presumptive detection of Legionella in potable,natural and industrial water. Detection is possible within an hour following the pre-concentration of a sample which can speed up the Legionella Control proceduresdramatically.

How the test works

The original water sample is concentrated by filtration or similar method and this prepared sample is eluted anddispensed into the test cuvette. A suspension of Legionella/binding magnetic beads is added. Legionella cells present in the prepared sample will bind to theantibodies immobilized onto the surface of the beads, to form bacteria/bead complexes. As these complexes can be separated by a magnet, they can be easily washed and suspended. Next the complexes are incubated with an enzyme-conjugated anti-Legionella antibody to form labelled complexes. After the washing steps, the complexes are visualized by the colorimetric reaction whenenzyme substrates are added.

It is quite possible that Legipid will give a positive result whereas culture gives a false negative. Where Legipid and culture results can be different, the following could be the reason:

1) Legionella is non culturable (VBNC)

After a dose of chlorine,Legionella bacteria can go into shock (wounded) state which is described as viable but non culturable (VBNC). Legipid will give a positive (reduced signal) in the presence of VBNC while culture will give a negative. PCR would give a positive.

2) Presence of growth inhibitors

The chlorination may not have been 100% effective and there could be pseudomonads present (often they co-exist in the presence of Legionella). Pseudomonads can also prevent the growth of Legionella on plates, sometimes this is very obvious, but not every Lab would automatically report on growth of a non-target organism. A dose of chlorine could also disperse a high count of pseudomonads living in any biofilm present within the water system; they may not have shown up in high volume in tests before remediation.


3) Time delay

The Legipid tests would have been carried out immediately, however the culture tests would have been some time later. Were the samples sent to the lab using Thiosulphate sample bottles? If not, it is possible that the neutralisation was not 100% effective and some residual chlorine continued to kill any remaining live cells before they reached the plate.

What you can be sure of is that there is no smoke without fire and if Legipid has given a positive result then there must be some Legionella present! In these rare instances, Aqua Analyse will discuss the likely reasons and agree a course of action to suit the circumstances and steps forward to ensure the system is totally protected.

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