S14: Practical approaches for Legionella control

Legionella pneumophila is an ubiquitous bacteria that causes respiratory disease following inhalation and is typically disseminated via contaminated water droplets from an artificial water reservoir.  Legionella requires the presence of a protozoan host, such as amoebae, to replicate in the environment due to very specific nutritional requirements.  There is an expanding body of literature reporting that this replication requirement by Legionella complicates the treatment of this bacterium by biocides.  Examining previously published literature on the effects of host/Legionella interactions and ongoing comparative co-culture experiments, it has been observed that biocides with an oxidizing mechanism of action are more affected by the environmental form of Legionella replication than non-oxidizing biocide.  It is hypothesized that the upregulation of Legionella genes that encode for proteins that can protect the bacterium against oxidative damage may be the mechanism that explains the susceptibility dichotomy.  Follow-up studies examining the differing abilities of oxidizing and non-oxidizing biocides to control planktonic and sessile Legionella in a mixed co-culture biofilm reactor confirm the heightened ability of non-oxidizing biocides to control Legionella relative to an oxidizing biocide treatment regime.  Further studies should be taken to examine how current tower treatment protocols can be amended to drive increased biocide performance against Legionella.