Ecology of Legionella pneumophila within water distribution systems.

The reservoir for hospital-acquired Legionnaires disease has been shown to be the potable water distribution system. We investigated the influence of the natural microbial population and sediment (scale and organic particulates) found in water systems as growth-promoting factors for Legionella pneumophila. Our in vitro experiments showed that: (i) water from hot-water storage tank readily supported the survival of L. pneumophila, (ii) the concentration of sediment was directly related to the survival of L. pneumophila, (iii) the presence of environmental bacteria improved the survival of L. pneumophila via nutritional symbiosis, (iv) the combination of sediment and environmental bacteria acted synergistically to improve the survival of L. pneumophila, and (v) the role of sediment in this synergistic effect was determined to be nutritional. Sediment was found to stimulate the growth of environmental microflora, which in turn stimulated the growth of L. pneumophila. These findings confirm the empiric observations of the predilection of L. pneumophila for growth in hot-water tanks and its localization to sediment. L. pneumophila occupies an ecological niche within the potable water system, with interrelationships between microflora, sediment, and temperature.