Influence of Temperature on Growth of Four Different Opportunistic Pathogens in Drinking Water Biofilms

High drinking water temperatures occur due to climate change and could enhance the growth of opportunistic pathogens in drinking water systems. We investigated the influence of drinking water temperatures on the growth of Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Mycobacterium kansasii and Aspergillus fumigatus in drinking water biofilms with an autochthonous microflora. Our results reveal that the growth of P. aeruginosa and S. maltophilia in the biofilm already occurred at 15.0 °C, whereas M. kansasii and A. fumigatus were able to grow when temperatures were above 20.0 °C and 25.0 °C, respectively. Moreover, the maximum growth yield of P. aeruginosa, M. kansasii and A. fumigatus increased with increasing temperatures up to 30 °C, whereas an effect of temperature on the yield of S. maltophilia could not be established. In contrast, the maximum ATP concentration of the biofilm decreased with increasing temperatures. We conclude from these results that high drinking water temperatures caused by, e.g., climate change can result in high numbers of P. aeruginosa, M. kansasii and A. fumigatus in drinking water systems, which poses a possible risk to public health. Consequently, it is recommended for countries with a more moderate climate to use or maintain a drinking water maximum standard temperature of 25 °C.