Effects of Disinfection on Legionella spp., Eukarya, and Biofilms in a Hot Water System

Legionella species are frequently detected in hot water systems, attached to the surface as a biofilm. In this work, the dynamics ofLegionella spp. 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 ofLegionella and eukarya were investigated by small-subunit (SSU) ribosomal cloning and sequencing. Our results showed that pathogenicLegionella species remained after the heat shock and chemical treatments (Legionella pneumophila andLegionella 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 (Thecamoebae sp.,Vannella sp., andHartmanella vermiformis ) and after the first heat shock treatment, but onlyH. vermiformis remained. 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, effectiveLegionella disinfection may be dependent on the elimination of these important microbial components. We suggest that eradicatingLegionella in hot water networks requires better study of bacterial and eukaryal species associated withLegionella in biofilms.