Survival and growth of Legionella pneumophila in both biofilm and planktonic phases were determined with a two-stage model system. The model used filter-sterilized tap water as the sole source of nutrient to culture a naturally occurring mixed population of microorganisms including virulent L. pneumophila. At 20°C, L. pneumophila accounted for a low proportion of biofilm flora on polybutylene and chlorinated polyvinyl chloride, but was absent from copper surfaces. The pathogen was most abundant on biofilms on plastics at 40°C, where it accounted for up to 50% of the total biofilm flora. Copper surfaces were inhibitory to total biofouling and included only low numbers of L. pneumophila organisms. The pathogen was able to survive in biofilms on the surface of the plastic materials at 50°C, but was absent from the copper surfaces at the same temperature. L. pneumophila could not be detected in the model system at 60°C. In the presence of copper surfaces, biofilms forming on adjacent control glass surfaces were found to incorporate copper ions which subsequently inhibited colonization of their surfaces. This work suggests that the use of copper tubing in water systems may help to limit the colonization of water systems by L. pneumophila.

A two-stage chemostat model of a plumbing system was developed, with tap water as the sole nutrient source. The model system was populated with a naturally occurring inoculum derived from an outbreak of Legionnaires' disease and containing Legionella pneumophila along with associated bacteria and protozoa. The model system was used to develop biofilms on the surfaces of a range of eight plumbing materials under controlled, reproducible conditions. The materials varied in their abilities to support biofilm development and the growth of L. pneumophila. Elastomeric surfaces had the most abundant biofilms supporting the highest numbers of L. pneumophila CFU; this was attributed to the leaching of nutrients for bacterial growth from the materials. No direct relationship existed between total biofouling and the numbers of L. pneumophila CFU.

Biofilms containing diverse microflora were developed in tap water on glass and polybutylene surfaces. Legionella pneumophila within the biofilms was labelled with monoclonal antibodies and visualized with immunogold or fluorescein isothiocyanate conjugates. Development of a differential interference contrast * Corresponding author.

A three-stage chemostat containing a mixed consortium of microorganisms, including Legionella pneumophila, was used to determine the suitability of a silver-containing paint to control biofouling in water systems. The paint was efficient in controlling total surface colonisation by heterotrophic microorganisms and growth of the pathogen over a 2-week period. Biodiversity was limited in the presence of the silver paint and this was thought to help control L. pneumophila numbers. Glass control tiles suspended alongside the silver painted tiles also had reduced colonisation for the 2-week period, suggesting that low levels of silver leached from the paint surface. This loss of silver was confirmed since the inhibition of biofouling and inclusion of the pathogen was not maintained after the 2-week period. Although this paint was unsuitable for controlling biofouling over extended time periods, the data suggest that a reformulated paint or electrochemical method of introducing silver ions may be successful.

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