Oportunistic pathogenic microorganisms in drinking water

Because of the expected climate change, it is probable that in the future the earth’s warming will lead to a rise in the temperature of surface water, water distribution systems and pipe installations. Opportunistic pathogenic microorganisms, which are capable of growing in drinking water, are often adapted to higher temperatures. As temperatures rise, these organisms could therefore occur more frequently in the microbial populations in drinking-water related environments.

On the basis of a previous BTO project, quantitative PCR methods were developed for the specific detection of opportunistic pathogenic microorganisms that present a possible health risk in the Netherlands. These involved fungi (Aspergillus fumigatus) and mycobacteria (Mycobacterium avium, Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Acanthamoeba spp.).

The objective of the project is to discover whether the above-mentioned opportunistic pathogenic microorganisms occur in distributed drinking water, and whether the season (winter versus summer) has an influence on the counts.

Sampling drinking water at about ten locations

In 2010, we sampled drinking water in the summer and winter at about ten locations in the distribution systems of Leeuwarden, Breda, Almere, ps Scheveningen, ps Kralingen, ps Berenplaat, ps Weesperkarpsel and ps Andijk. In the summer, purified water samples were also collected at the respective pumping stations. Most of the drinking water samples were taken from the distribution system; the summer drinking water samples from ps Kralingen and ps Berenplaat came from indoor installations in buildings.

The drinking water samples were analysed for temperature, colony counts at 22 ⁰C and 37 ⁰C, colony formation units of Legionella, P. aeruginosa and Aeromonas at 30 ⁰C and 37 ⁰C, ATP, cell counts, and the number of gene copies of fungi, A. fumigatus, and mycobacteria, M. avium, P. aeruginosa, S. maltophilia, Acanthamoeba spp. and Legionella pneumophila.

Fungi and mycobacteria: generalised in Dutch drinking water

Based on the results, we concluded that fungi and mycobacteria generally occur in drinking water in the Netherlands, and are capable of multiplying in distribution systems and indoor installations. Drinking water temperatures between 5oC and 22⁰C have no influence on the number of fungi and mycobacteria in distributed water. P. aeruginosa, S. maltophilia and A. fumigatus occur sporadically in drinking water, and appear to be capable of multiplying in distribution systems and/or indoor installations. Drinking water temperatures around 20⁰C result in higher counts of S. maltophilia and A. fumigatus than at temperatures around 7⁰C. It is still unclear whether the occurrence of the fungi strains A. fumigatus, and mycobacteria strains P. aeruginosa and S. maltophilia, in drinking water are actually pathogenic for humans.