title: Longitudinal evaluation of the efficacy of heat treatment procedures against Legionella spp. in hospital water systems by using a flow cytometric assay.
abstract: Legionella spp. are frequently isolated in hospital water systems. Heat shock (30 min at 70°C) is recommended by the World Health Organization to control its multiplication. The aim of the study was to evaluate retrospectively the efficacy of heat treatments by using a flow cytometry assay (FCA) able to identify viable but nonculturable (VBNC) cells. The study included Legionella strains (L. pneumophila [3 clusters] and L. anisa [1 cluster]) isolated from four hot water circuits of different hospital buildings in Saint-Etienne, France, during a 20-year prospective surveillance. The strains recovered from the different circuits were not epidemiologically related, but the strains isolated within a same circuit over time exhibited an identical genotypic profile. After an in vitro treatment of 30 min at 70°C, the mean percentage of viable cells and VBNC cells varied from 4.6% to 71.7%. The in vitro differences in heat sensitivity were in agreement with the observed efficacy of preventive and corrective heating measures used to control water contamination. These results suggest that Legionella strains can become heat resistant after heating treatments for a long time and that flow cytometry could be helpful to check the efficacy of heat treatments on Legionella spp. and to optimize the decontamination processes applied to water systems for the control of Legionella proliferation.
authors.affiliation: Groupe Immunité des Muqueuses et Agents Pathogènes, EA 3064, Unité d'Hygiène, Centre Hospitalo-Universitaire de Saint-Etienne, 42055 Saint-Etienne Cedex 02, France.
authors.forename: Severine
authors.initials: S
authors.lastname: Allegra
authors.forename: Florence
authors.initials: F
authors.lastname: Grattard
authors.forename: Françoise
authors.initials: F
authors.lastname: Girardot
authors.forename: Serge
authors.initials: S
authors.lastname: Riffard
authors.forename: Bruno
authors.initials: B
authors.lastname: Pozzetto
authors.forename: Philippe
authors.initials: P
authors.lastname: Berthelot
mesh_terms: D015169:Colony Count, Microbial; D004203:Disinfection / Q000379:methods*; D004784:Environmental Monitoring / Q000379:methods; D005434:Flow Cytometry / Q000379:methods*; D005602:France; D006785:Hospitals, University; D006358:Hot Temperature; D007875:Legionella / Q000254:growth & development* / Q000302:isolation & purification; D016133:Polymerase Chain Reaction; D014867:Water / Q000032:analysis; D014871:Water Microbiology; D014881:Water Supply
chemical_list: D014867:Water