Development of a pilot-scale 1 for Legionella elimination in biofilm in hot water network: heat shock treatment evaluation.
OBJECTIVE
(i) To develop an analytical tool in order to evaluate the effectiveness of anti-Legionella treatment in biofilm and (ii) study the fate of Legionella populations in water and biofilm after applying a heat shock treatment.


RESULTS
A pilot-scale unit simulating a hot water system was built and designed by the Scientific and Technical Building Centre (CSTB, France). At the end of the contamination period, a stable cultivable Legionella spp. concentration of 5x10(5) CFU l(-1) was obtained. Two heat shock treatments (70 degrees C for 30 min) were applied. The results showed that the first treatment had a transitional effect on the abatement of Legionella concentrations, while the second treatment had no detectable effect on Legionella populations in water and biofilm. The DAPI (4',6'-diamidino-2-phenylindole), Legionella PCR and GVPC (glycocolle vancomycin pyrophosphate cycloheximide) counts measured in the dead leg water of the Test Loop were 1, 2 and 2 log units higher than results found in the Test Loop water. Moreover, Legionella spp. count in tap water was about 10(4) GU l(-1). These analyses revealed that they are responsible for the rapid recolonization as well as the uncomplete destroyed biofilm. In addition, a resistance test was conducted and showed that Legionella in the second heat shock treatment was not thermo-resistant but thermo-acclimated.


CONCLUSIONS
Thermal disinfection does not seem to be efficient enough to eliminate Legionella when it is used as a curative treatment.


CONCLUSIONS
This work could help water managers for a better management of water network and for a better control of Legionella.
 Centre Scientifique et Technique du Bâtiment, Marne-la-Vallée cedex 02, France.| Laboratoire de Chimie et de Microbiologie de l'Eau, Université de Poitiers, Poitiers, France.
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M
Farhat
 Centre Scientifique et Technique du Bâtiment, Marne-la-Vallée cedex 02, France.
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MC
Trouilhé
 Direction Générale de la santé, Bureau EA2 - Environnements intérieurs, milieux de travail et accidents de la vie courante, Paris, France.
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E
Briand
 Centre Scientifique et Technique du Bâtiment, Marne-la-Vallée cedex 02, France.
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M
Moletta-Denat
 Centre Scientifique et Technique du Bâtiment, Marne-la-Vallée cedex 02, France.
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E
Robine
 Laboratoire de Chimie et de Microbiologie de l'Eau, Université de Poitiers, Poitiers, France.
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J
Frère
D018441:Biofilms / Q000254:growth & development*; D015169:Colony Count, Microbial; D004203:Disinfection / Q000379:methods*; D006358:Hot Temperature; D007875:Legionella / Q000254:growth & development*; D010865:Pilot Projects; D014871:Water Microbiology; D014873:Water Pollutants / Q000032:analysis; D018508:Water Purification / Q000379:methods*
D014873:Water Pollutants