Members of the
Legionella genus find suitable conditions for their growth and survival in nuclear power plant cooling circuits. To limit the proliferation of
Legionella pathogenic bacteria in nuclear power plant cooling circuits, and ensure that levels remain below regulatory thresholds, monochloramine treatment can be used. Although the treatment is highly effective,
i.e. it reduces
Legionella numbers by over 99%,
Legionella bacteria can still be detected at low concentrations and rapid re-colonisation of circuits can occur after the treatment has ceased. The aim of this study was to develop an
in vitro methodology for determining the intrinsic susceptibility of
L. pneumophila strains, collected from various nuclear power plant cooling circuits subjected to different treatment conditions. The methodology was developed by using an original approach based on response surface methodology (RSM) combined with a multifactorial experimental design. The susceptibility was evaluated by the Ct factor. The susceptibility of environmental strains varies widely and is, for some strains, greater than that of known tolerant species; however, strain susceptibility was not related to treatment conditions. Selection pressure induced by monochloramine use did not result in the selection of more tolerant
Legionella strains and did not explain the detection of
Legionella during treatment or the rapid re-colonisation of cooling circuits after disinfection has ceased.
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