Inactivation and sub-lethal injury of salmonella typhi, salmonella typhimurium and vibrio cholerae in copper water storage vessels

Background: This study provides information on the antibacterial effect of copper against the water-borne pathogens Salmonella Typhi, Salmonella Typhimurium and Vibrio cholerae. Methods: Suspensions of each pathogen were kept in water within a traditional copper vessel at 30°C for 24 h. Samples were withdrawn, diluted and plated onto suitable growth media. Conventional enumeration of healthy (uninjured) bacteria was carried out using standard aerobic incubation conditions. Additionally, reactive oxygen species-neutralised (ROS-n) conditions were achieved by adding the peroxide scavenger sodium pyruvate to the medium with anaerobic incubation, to enumerate uninjured (ROS-insensitive) and injured (ROS-sensitive) bacteria. Differences between log-transformed means of conventional (aerobic) and ROS-n counts were statistically evaluated using t tests. Results: Overall, all three pathogens were inactivated by storage in copper vessels for 24 h. However, for shorter-term incubation (4-12 h), higher counts were observed under ROS-n conditions than under aerobic conditions, which demonstrate the presence of substantial numbers of sub-lethally injured cells prior to their complete inactivation. Conclusions: The present study has for the first time confirmed that these bacterial pathogens are inactivated by storage in a copper vessel within 24 h. However, it has also demonstrated that it is necessary to account for short-term sub-lethal injury, manifest as ROS-sensitivity, in order to more fully understand the process. This has important practical implications in terms of the time required to store water within a copper vessel to completely inactivate these bacteria and thereby remove the risk of water-borne disease transmission by this route

Oxygen and photoinactivation of Escherichia in UVA and sunlight

Aims: To establish the influence of oxygen on Escherichia coli before, during and after exposure to UVA orsimulated sunlight. Methods and Results: Bacterial suspensions were exposed either to UVA or simulated sunlight. Conventional aerobic plate counts of illuminated cell suspensions were consistently lower than those obtained under conditions where reactive oxygen species (ROS) were neutralized, either (i) by the addition of the peroxide scavenger sodium pyruvate (0.05% w/v) to the medium with subsequent incubation in an anaerobic jar or (ii) by culturing on a prereduced medium within an anaerobic cabinet, indicating that a substantial proportion of such cells are sublethally injured. While the presence of oxygen during the growth period resulted in a greater resistance of aerobically grown cells to simulated sunlight compared with their anaerobic counterparts, the extent of inactivation during illumination was directly related to the dissolved oxygen content of the water. Conclusions: The results show that, at each stage, oxygen has a marked influence on the observed colony count. Significance and Impact of the Study: Overall, the results indicate that future studies of bacteria exposed to UVA or sunlight should consider the effects of oxygen at every stage in the procedure, and especially during enumeration, where the inhibitory effects of ROS must be neutralized in order to obtain a valid count. An investigation of the effects of ROS neutralization on the counts of faecal bacteria under field conditions in natural waters is now required to establish the significance of these finding to solar water treatment

Oxygen and photoinactivation of Escherichia in UVA and sunlight

Aims: To establish the influence of oxygen on Escherichia coli before, during and after exposure to UVA orsimulated sunlight. Methods and Results: Bacterial suspensions were exposed either to UVA or simulated sunlight. Conventional aerobic plate counts of illuminated cell suspensions were consistently lower than those obtained under conditions where reactive oxygen species (ROS) were neutralized, either (i) by the addition of the peroxide scavenger sodium pyruvate (0.05% w/v) to the medium with subsequent incubation in an anaerobic jar or (ii) by culturing on a prereduced medium within an anaerobic cabinet, indicating that a substantial proportion of such cells are sublethally injured. While the presence of oxygen during the growth period resulted in a greater resistance of aerobically grown cells to simulated sunlight compared with their anaerobic counterparts, the extent of inactivation during illumination was directly related to the dissolved oxygen content of the water. Conclusions: The results show that, at each stage, oxygen has a marked influence on the observed colony count. Significance and Impact of the Study: Overall, the results indicate that future studies of bacteria exposed to UVA or sunlight should consider the effects of oxygen at every stage in the procedure, and especially during enumeration, where the inhibitory effects of ROS must be neutralized in order to obtain a valid count. An investigation of the effects of ROS neutralization on the counts of faecal bacteria under field conditions in natural waters is now required to establish the significance of these finding to solar water treatment

A generic, process-based model of microbial pollution in aquatic systems

Based on a comprehensive synthesis of data available within the literature, a new process-based model of microbial pollution is presented, which is applicable for surface and coastal waters. The model is based on a generic set of parameterisations that describe the dynamics of most protozoan, bacterial and viral organisms of interest, including pathogens and microbial indicator organisms. The parameterisations dynamically account for the effects of temperature, salinity, pH, dissolved oxygen, sunlight, nutrients and turbidity on the growth and mortality of enteric organisms. Parameters for a range of organisms are also presented which are based on collation of literature data. The model has been implemented within an aquatic ecology model, Computational Aquatic Ecosystem Dynamics Model (CAEDYM), which can couple to multidimensional hydrodynamic models. Without adjustment of the literature derived parameter values, a 3-D implementation is validated against observed data from three freshwater systems that differ in their climatic zone, trophic status and operation. The simulations highlight the spatial and temporal variability that may be encountered by operators. Additionally, large differences in the fate and distribution of different species originate from variable rates of growth, mortality and sedimentation and it is emphasized that the use of surrogates for quantifying risk is problematic. The model can be used to help design targeted monitoring programs, explore differences between species, and to support real-time decision-making. Areas where insufficient understanding and data exist are discussed.Matthew R. Hipsey, Jason P. Antenucci, Justin D. Brooke