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Seventh Research Framework Programme (FP7)

Marie-Curie Action

Marie Curie Industry-Academia Partnerships and Pathways (IAPP)

Vesicount Project
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Vesicount project

The VESICOUNT project, which full title is "Methods for the quantification of suspended protozoa vesicles containing Legionella in water environments", is a Marie Curie Action, in the Marie Curie Industry-Academia Partnerships and Pathways program.

This four year's' project started October 1st 2008

Project overview

A significant number of legionellosis outbreak is related to industrial complexes and cooling towers. The risk for a person to contract a legionellosis is not systematic, but depends on numerous parameters, amongst them figuring the concentration of Legionella in a hydro-environment, the virulence of the strain, the means of the vaporization, the time of exposure and the individual susceptibility of the exposed person. For the time being, the exact composition of a contaminating aerosol is not known. This last one might contain just one or more bacteria, the fragments of a Legionella contaminated biofilm, vesicles expulsed by amebas containing Legionella, the amebas themselves that are infected with Legionella. Still, during their natural biological lifecycle, amebas are capable of liberating vesicles containing Legionella transporting them to the location of the infection. Knowing that the diameter of one vesicle is of 2.1 to 6.4 μm, containing up to 90% of Legionella (1 to 5 μm), they might contain several hundreds of viable bacteria. More, it was suggested that vesicle could be itself an infecting agent.

The capacity of Legionella to be infected and to multiply inside of a protozoa is one of its critical factors for their survival. As a matter of fact, they are able to protect themselves from the deleterious action of disinfectants, biocides and other stressing environmental conditions. By harbouring Legionella, the protozoa accelerate the growth of these bacteria inside of air conditioning installations

The current insufficiencies concerning the Legionella risk assessment particularly in industrial installations are situated on two different levels:

First concerning the diagnostic of a Legionella contamination itself, an important difference of sensitivity of the diagnostic methods has been stated. Namely the PCR (polymerase chain reaction) and the classic culture do not give clear results as the analysis graphs show an important shifting. One of the explanations for this phenomenon could be the fact, that the protozoa remain stuck to the walls, whereas the vesicles ejected by the protozoa circulate. With the help of the PCR all the Legionella are counted, whereas with the classic culture one single opened vacuole will be at the source of the colony and will give only one single colony forming unit (cfu) UFC.

Secondly, there remain unresolved challenges on the treatment level once aLegionella contamination has been stated. The problem here resides in the fact that neither physical nor chemical biocides seem to operate in a satisfying way.

The final objective is the elaboration of a basis for a possible standard in the field: "how to accurately measure and control the number of Legionellae in presence of protozoa, with respect to the dissemination potential and risk analysis".

Vesicount is intended to be a European joint cooperation programme permitting a cross fertilisation that is all at once transnational and interdisciplinary as partners from different universes (medicine, engineering, industrial application) work on one single problem in order to contribute to progress in the field of Legionella detection and risk assessment. The different but still complementary points of view engender a knowledge transfer in a sense that industry could express its needs and problems encountered in practice. On the other hand, university can valorise its research and knowledge by introducing it into a practical field of application.

Updated : November 2012