ABSTRACTLegionellaspecies are frequently detected in hot water systems, attached to the surface as a biofilm. In this work, the dynamics ofLegionellaspp. and diverse bacteria and eukarya associated together in the biofilm, coming from a pilot scale 1 system simulating a real hot water system, were investigated throughout 6 months after two successive heat shock treatments followed by three successive chemical treatments. Community structure was assessed by a fingerprint technique, single-strand conformation polymorphism (SSCP). In addition, the diversity and dynamics ofLegionellaand eukarya were investigated by small-subunit (SSU) ribosomal cloning and sequencing. Our results showed that pathogenicLegionellaspecies remained after the heat shock and chemical treatments (Legionella pneumophilaandLegionella anisa, respectively). The biofilm was not removed, and the bacterial community structure was transitorily affected by the treatments. Moreover, several amoebae had been detected in the biofilm before treatments (Thecamoebaesp.,Vannellasp., andHartmanella vermiformis) and after the first heat shock treatment, but onlyH. vermiformisremained. However, another protozoan affiliated with Alveolata, which is known as a host cell forLegionella, dominated the eukaryal species after the second heat shock and chemical treatment tests. Therefore, effectiveLegionelladisinfection may be dependent on the elimination of these important microbial components. We suggest that eradicatingLegionellain hot water networks requires better study of bacterial and eukaryal species associated withLegionellain biofilms.

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Aims:  (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. Methods and 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 5 × 105 CFU l−1 was obtained. Two heat shock treatments (70°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 104 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. Conclusion:  Thermal disinfection does not seem to be efficient enough to eliminate Legionella when it is used as a curative treatment. Significance and Impact of the Study:  This work could help water managers for a better management of water network and for a better control of Legionella.

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This article outlines a comprehensive analysis of the microbial diversity of aerosols produced during screening in a green waste composting plant using both culture and molecular techniques. Bacteria, thermophilic actinomycetes and fungi were quantified in the aerosols. The structure of the microbial community was examined using a fingerprint technique and DNA libraries. The results show: (i) the very high diversity of bacteria and fungi in aerosols produced during the composting screening stage, (ii) the low percentage of cultivability for bacteria in aerosols, (iii) the abundance of Thermoactinomyces spp. and Aspergillus spp. in compost aerosols.