Biofilm formation of Legionella pneumophila in a pilot-scale water re-circulation system.

OBJECTIVE To develop a novel pilot-scale water re-circulation system to evaluate the potential of Legionella biofilm colonied in water distribution system and to assess the effect of flow regimes(laminar vs stagnant)on the presence of Legionella within the biofilm.METHODS Culture techniques and confocal laser scanning microscopy were used to monitor the process of Legionella attachment to the surface of re-circulation loops and formation of the biofilm.RESULTS After 5 weeks of adhesion and multiplication of the Legionella pneumophila,a stable ecosystem in the pilot-scale water re-circulation system was established,more than 95.8% Legionella strains contained in the biofilm.Colonization of Legionella in biofilms was significantly higher in the re-circulation loops(7.8×104 CFU/cm2),comparing with the dead legs(1.5×103 CFU/cm2).CONCLUSIONS L.pneumophila biofilms are successfully established in pilot-scale water systems.The biofilms play an important role in proliferation of Legionella.The results also reveal that stagnation will not promote the growth of Legionella.