Abstract
Within the biofilm and scales Legionella is less far susceptible to the effects of the most frequently used biocides. The objective of this study was to evaluate the effect of a 4-months continuous injection of a gas mixture (CO2 and inert gas) in the hot water distribution system of a large hotel colonized by L. pneumophila sg3 on limiting biofilm formation and scales and in turn Legionella growth. Before the continuous injection of the gas mixture, out of the 15 sampling points examined every month 60% were colonized by Legionella (mean concentrations of 102 cfu/L in the boilers and the return loop, and 10 4 cfu/L in taps and showers). One week after the injection of the gas mixture and daily fluxing of the distal outlets, the level of colonization decreased ( 10 4 cfu/L) in all the sampling points. Thus, cleaning of the boilers was performed and distal outlets were again fluxed daily. One week after the level of contamination decreased again ( 10 4 cfu/L. Results indicate that the gas mixture was able to reduce the level of colonization by Legionella only because associated to the fluxing of the distal outlets.
Highlights
Legionnaires’ disease is known to cause community-acquired pneumonia and may occur, sporadically or as part of an outbreak, as travel-associated infection [1] [2]
Among the antimicrobial agents monochloramine seems to be more effective for decreasing Legionella within the biofilms in vitro as well as in model plumbing systems [4]-[6]
Due to the length of the water distribution systems (WDS) the heat loss was high, so the temperature of the monitored hot water samples ranged between 45 ̊C and 55 ̊C
Summary
Legionnaires’ disease is known to cause community-acquired pneumonia and may occur, sporadically or as part of an outbreak, as travel-associated infection [1] [2]. It is well known that biofilm formation in plumbing systems is a microbial survival strategy that uses extracellular secretions to entrap and concentrate nutrients. Among the antimicrobial agents monochloramine seems to be more effective for decreasing Legionella within the biofilms in vitro as well as in model plumbing systems [4]-[6]. It has been suggested that water characteristics, such as trace element concentrations, hardness and accumulation of inorganic contaminants can cause many negative effects on drinking water quality, by offering nutrients and surface area for Legionella to grow and by protecting bacteria from disinfectants [7] [8]. It could be supposed that treatments targeting the removal of scales and biofilm on water distribution systems (WDS) may be effective at reducing Legionella colonization
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