Date Published: June 19, 2018
Publisher: Springer Berlin Heidelberg
Author(s): Yi Wang, Pramod Pandey, Yawen Zheng, Edward Robert Atwill, Gregory Pasternack.
Improved understanding of pathogen survival in the stream environment is needed to enhance existing predictive models of stream pathogen populations. Further, the increasing use of thermal springs for bathing necessitates additional studies focused on not only typical streams but also thermal spring conditions, where water temperature is relatively higher than typical streams. This study was conducted to assess the survival of E. coli O157:H7 and Salmonella Typhimurium in stream water under free floating and particle-attached conditions at a range of temperature. A series of microcosm studies were conducted to determine pathogen decay rates. In bench-scale experiments, water circulation and sediment resuspension mimicked natural stream and thermal spring conditions, with continuous air flow providing aeration, constant mixing and turbulent conditions, and improved water circulation. Data on E. coli O157:H7 and Salmonella survival were subsequently used to determine first-order decay equations for calculating the rate constant and decimal reduction time for the modeled experimental conditions. Results showed that at 40 °C, the survival of particle attached E. coli O157:H7 was longer than that of particle attached Salmonella. Under free floating condition, Salmonella survived longer than E. coli O157:H7. At 50 °C, survival of particle attached E. coli O157:H7 and Salmonella was longer than that of free floating E. coli and Salmonella. At 60 °C, survival of particle attached Salmonella was longer than that of free floating Salmonella. Similarly at 60 °C, the survival of E. coli O157:H7 under particle attached condition was longer than that of the free floating condition. The findings of this study suggest that the survival of E. coli O157:H7 differs than the survival of Salmonella in stream water and thermal spring conditions, and the assumption used in previous studies to estimate survival of bacteria in stream environment could result in over/underestimation if the impact of particle attachment on pathogen survival is not accounted for.
The abundant pathogenic bacteria in ambient water bodies such as rivers, lakes, reservoirs, coasts and estuaries is a serious worldwide concern. As a form of pollution, pathogenic bacteria pose risks to human and animal health (Abia et al. 2016; Eichmiller et al. 2014; Pandey et al. 2016; Payment et al. 2000). In streams, these bacteria are reported to be in free floating condition, as well as in particle attached condition (Burton et al. 1987; Eichmiller et al. 2014; Munro et al. 2016; Pandey and Soupir 2013). Attachment to sediment particles changes bacteria survival and transport (Pandey et al. 2012).
To understand E. coli and Salmonella survival in streams, a series of experiments were executed at multiple temperatures (Fig. 1) representing typical stream and thermal spring water temperature conditions. Experiments were performed in microcosms containing streambed sediment and stream water. The sediment was collected from the streambed. Water was collected from overlying water in streams. The sediment and water samples were collected from 10 randomly selected locations in four sub-watersheds of Merced River in Central Valley of California, USA. These sub-watersheds include (from downstream to upstream): Ingalsbe Slough-Merced River Watershed, Maxwell Creek-Merced River Watershed, Bear Creek-Merced River Watershed, and Yosemite Creek-Merced River Watershed. Sediment samples (approximately 20 g from each location) were mixed to create a composite sediment bed (≈ 3 cm depth; ≈ 200 g weight) in microcosms for inactivation study. Similarly, water samples (100 mL from each location) from 10 different locations were mixed to create a composite stream water column (≈ 10 cm depth) in microcosms.Fig. 1Experiment sketch of microcosm study (left shows the microcosm of sediment and water column, and right shows water column microcosm)
The results of this study suggest that the time required for pathogen reduction at a temperature (either typical streams or thermal spring) could be higher when stream water has suspended particles, depending on the ambient temperature. These results align with previous research (Abia et al. 2016; Bai and Lung 2005; Burton et al. 1987; Havelaar et al. 1995; Mueller-Spitz et al. 2010), which suggested that sediment particles provide favorable environments for the survival of bacteria such as E. coli, Salmonella, V. cholerae and S. dysenteriae.