Summary
The ability of Legionella pneumophila to colonise domestic water systems is a primary cause of outbreaks of Legionnaire's
disease in humans. World Health Organization guidelines recommend that drinking water
is chlorinated to between 0.2 and 1 mg/L [Chlorine in drinking-water. Guidelines for drinking-water quality, 2nd edn. Geneva: World Health Organization; 1996], but L. pneumophila is repeatedly isolated from chlorinated water systems, indicating that this treatment
is not effective at preventing colonisation. Current UK guidelines recommend a one-off
treatment of 20–50 mg/L of free chlorine to remove the bacteria. In this study we report on the persistence
of L. pneumophila serogroup 1 in a domestic shower system despite repeated cycles of chlorination at
50 mg/L for 1 h exposure time, over the course of two and a half years. Persisting isolates were
subjected to in-vitro phenotypic analyses and polymerase chain reaction analysis for
the toxin-encoding mip gene. Random amplified polymorphic DNA typing was also performed to determine whether
the isolates recovered on different occasions were the same strain. We found that
seven isolates of L. pneumophila recovered over a two-and-a-half year period are the same genetically defined strain,
indicating that the bacteria can persist despite repeated cycles of chlorination after
each successive isolation.
Keywords
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Article info
Publication history
Published online: May 17, 2010
Accepted:
June 13,
2008
Received:
June 2,
2008
Identification
Copyright
© 2008 The Hospital Infection Society. Published by Elsevier Inc. All rights reserved.
