Organic compounds in water are energy and carbon sources for heterotrophic bacteria. Only a small proportion of dissolved organic carbon (DOC), less than 5%, is utilized by heterotrophs. Previous studies show the concentration of biodegradable organic matter in drinking water is often the critical factor that determines the rate of growth of heterotrophic bacteria in water distribution systems. Standardized tests (e.g. assumable organic carbon (AOC)) are a widely used indicators of bacterial regrowth potential in drinking water. Carbon concentrations (AOC and DOC) are not found to have a clear relationship to the presence/absence for many emerging pathogens, such as Pseudomonas aeruginosia and Stenotrophomonas maltophilia. In this study we explore how the composition of organic carbon influences the competitive growth of the three aforementioned emerging opportunistic pathogens and whether they are capable of growing competitively with indigenous, non-pathogenic bacteria in high and low water age conditions. With this aim we measured the fluorescence excitation-emission (EEMs) spectra and the concentration of amino acids (AAs) in two engineered water systems: (1) building CT systems and (2) a drinking water distribution (DWD) system. Organic carbon concentrations for these systems were found to follow the order: DWD (low water age) < DWD (high water age) ~ CT (low water age) < CT (high water age). Overall, preliminary results indicate that the mass of proteinaceous material generally increases with water age. Quantitative analyses of individual amino acids, revealed, in particular, elevated levels of cysteine, tyrosine, and phenylalanine in high water age samples from both systems. No arginine or proline were observed in low age water samples. AAs known to be essential for growth of L. pneumophila in vitro were found to increase in CTs as water was cycled and reused, which is analogous to water age. The concentration of AAs required for L. pneumophila growth in high water age was significantly greater (p<0.03) than in low water age for both CT and DWD systems. Elevated levels of serine and proline, two essential AAs for the growth of S. maltophilia, were observed in high water age CT and DWD samples. Updated results and the implications to the growth and selection of emerging pathogens will be presented.

Shawn McElmurry

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