A novel monitoring system for Legionella
Legionella species are gram-negative bacteria found in freshwater sources and can cause Pontiac fever or Legionnaires' disease, a severe pneumonia-driven multi-system condition. Large hot water systems such as cooling towers provide the ideal environment for the rapid expansion of Legionella bacteria which penetrate the pulmonary track through water droplets. Although factors such as bacterial concentration in water and strain virulence are probably implicated in Legionella outbreaks, the composition of the infective aerosol has not been extensively studied. Several reports show that protozoans naturally present in water favour the growth of Legionella bacteria or help the formation of Legionella-containing vesicles.The EU-funded 'Methods for quantification of free protozea vesicles containing legionella in a water environment' (VESICOUNT) project aimed to isolate and characterise the vesicles that get secreted from Legionella-infected protozoa such as amoebae. Researchers were able to identify 11 different types of vesicle-like structures and developed protocols to characterise them.A co-culture was set up between the most common environmental amoebae and a genetically modified strain of Legionella pneumophila which glows green, thereby facilitating its detection. Apart from vesicles containing live bacteria, researchers identified structures that resembled remnants of membranes and contained Legionella clusters.Measurements were performed over a four-month period in an industrial plant with two different cooling tower circuits. Data indicated that above 13 degrees Celsius protozoa were capable of entering the water system and identified certain system parameters that supported their growth. VESICOUNT work led to the identification and characterisation of elements releasedfrom the protozoa-Legionella co-existence in a water system. the methods devised by the project could be useful for water system monitoring.
Keywords
Water system, monitoring, Legionnaire's disease, Legionella pneumophila, protozoa, vesicles
