Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2007
Publication Date: 1/1/2008
Citation: McLaughlin, M.R., Brooks, J.P. 2008. EPA worst case water microcosms for testing phage biocontrol of Salmonella. Journal of Environmental Quality. 37:266-271.
Interpretive Summary: Phages are bacterial viruses that occur throughout the natural world and infect only specific bacteria. Scientific and commercial interest in using phages for biocontrol of bacterial diseases is growing. Recently a phage product received FDA approval for use in prevention and control of a human bacterial pathogen (Listeria) on meat and poultry products. Because bacterial contamination of meat, poultry and dairy products is frequently linked to fecal contamination, controlling human bacterial pathogens during animal production is often focused on manure management. In the work reported here, an innovative model system was developed, tested and described for simulating the environment of a swine manure lagoon without the problems of odor and other microbes found in lagoon effluent. The model used EPA worst case water, a defined medium approved for testing point of use water purifiers. Like effluent, the worst case water contained high levels of dissolved salts, organic carbon and turbidity. Control of Salmonella by phages was demonstrated in the worst case water model for the first time. The model provides researchers with a useful tool for studying phages and defining the requirements for their successful application to controlling specific bacterial pathogens, like Salmonella, in swine lagoons without affecting other microbes.
Technical Abstract: A microplate method was developed as a tool to test phages for their ability to control Salmonella in aqueous environments. The method used EPA (U.S. Environmental Protection Agency) worst case water (WCW) in 96-well plates. The WCW provided a consistent and relatively simple defined turbid aqueous matrix, high in total organic carbon (TOC) and total dissolved salts (TDS), to simulate swine lagoon effluent, without the inconvenience of malodor and confounding effects from other biological factors. The WCW was originally defined to simulate high turbidity and organic matter in water for testing point of use filtration devices. Use of WCW to simulate lagoon effluent for phage testing is a new and innovative application of this matrix. Control of physical and chemical parameters (TOC, TDS, turbidity, temperature and pH) allowed precise evaluation of microbiological parameters (Salmonella and phages). In a typical application, wells containing WCW were loaded with Salmonella enterica susp. enterica serovar Typhimurium (ATCC14028) and treated with phages alone and in cocktail combinations. Mean Salmonella inactivation rates (k, where the lower the value, the greater the inactivation) of phage treatments ranged from -0.79 to -1.44 versus -0.03 for Salmonella controls. Mean log10 reductions (the lower the value, the greater the inactivation) of Salmonella phage treatments were -1.21 for phage PR04-1, -2.14 for phage PR37-96, and -2.23 for both phages in a sequential cocktail, versus -0.03 for Salmonella controls. The WCW microcosm system was an effective tool for evaluating the biocontrol potential of Salmonella phages.