Legionella: a Biofilm Organism in Engineered Water Systems?

Abstract

Investigations of outbreaks of legionnaires disease have demonstrated that infection, in susceptible people, can occur by inhalation of water droplets containing viable legionellae. The appearance of the strain associated with disease in water in a building linked epidemiologically to the outbreak has been attributed in several instances to disturbance of the water system. As a result it has been postulated that legionellae may be associated with particulate matter and biofilms. New techniques for detecting legionellae in water samples by immunofluorescent microscopy (IFA) and systematic sampling were applied to two water systems linked with cases of disease. IFA results identified the location of the organism in each system—the biofilm adhering to the walls of a freshwater storage tank in a passenger ship and slime in the pond and pipework of two cooling towers.Legionella pneumophila was recoverable by culture only from water. IFA detected the organism in water and biofilms even when control measures such as chlorine and heat were used. These results confirm that L. pneumophila can colonise biofilms, hence long-term prevention of legionellosis will come only with knowledge of the factors governing formation and inhibition of biofilms in water systems.