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Title: Manure microbes may stop Salmonella in lagoons

item McLaughlin, Michael

Submitted to: Meeting Abstract
Publication Type: Popular Publication
Publication Acceptance Date: 12/18/2007
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Nontyphoidal Salmonella causes an estimated 1.4 million cases of human food-borne illness and more than 500 food-related human deaths in the United States annually. People infected with Salmonella, whether they experience typical symptoms of gastroenteritis and diarrhea or not, may be reservoirs from which the bacteria may be spread. Animals, including wild animals, domestic pets, and livestock are susceptible too, and can carry Salmonella and pass it in their manure. Like humans, pigs can be symptomless carriers. Commercial swine farm lagoons that constantly receive fresh manure from thousands of animals might be expected to be loaded with Salmonella, yet they are not. Salmonella, if it occurs at all, is found at such low levels in these environments that its detection often requires special cultural enrichment and DNA amplification techniques. Science has found a possible explanation for these low levels. Agricultural Research Service scientists, Mike McLaughlin and John Brooks studied bacteriophages, that had been obtained from swine manure lagoons. Bacteriophages are viruses that infect bacteria. They occur virtually everywhere and are estimated to be the most numerous life form on earth. They comprise many varieties, each restricted to infecting one or a few types of bacteria. Bacteriophages do not infect humans or other organisms. The bacteriophage study was conducted in 2006 at USDA’s Waste Management and Forage Research Unit at Mississippi State Mississippi. McLaughlin and Brooks tested two bacteriophages in carefully controlled laboratory experiments. They measured the Salmonella killing rates for the two bacteriophages alone and in sequential combinations. Results from the study, first reported at the 2006 International Annual Meeting of the Agronomy, Crop and Soil Science (Tri) Societies of America in Indianapolis, Indiana, were published in the Jan-Feb 2008 issue of the Journal of Environment Quality, a professional scientific journal of the Tri-societies. McLaughlin and Brooks devised a new laboratory test using EPA worst case water as a substitute for lagoon effluent in their experiments. Worst case water was originally designed to simulate high turbidity and organic matter in water and is an EPA-approved medium for testing point-of-use water filtration devices. The scientists used worst case water to simulate the high turbidity and organic matter of effluent, but without the malodor and confounding effects from other biological factors associated with real effluent. Control of physical and chemical parameters (total organic carbon, total dissolved solids, turbidity, temperature and pH) allowed precise evaluation of microbiological parameters (Salmonella and bacteriophage concentrations and combinations). Use of worst case water to simulate lagoon effluent for bacteriophage testing is a new and innovative application of this test matrix. Unlike traditional antibiotics and chemical disinfectants, which may have broad spectrum adverse consequences for other microbes, bacteriophages target specific bacteria, do not harm other life forms, and do not change the chemistry of the treated environment. In addition, because single bacteriophages infecting target bacterial cells, multiply a hundred fold or more and rupture the target cells, the bacteriophage replenish themselves and do not require repeated doses. McLaughlin noted “Bacteriophages are one of nature’s biocontrol mechanisms for bacteria. The presence of Salmonella-specific bacteriophages in the swine manure lagoons may help explain why Salmonella levels remain relatively low in these environments.” This research provided waste management scientists with a new and useful tool for studying bacteriophages. The study defined requirements for the use of specific bacteriophages in controlling Salmonella, and helps explain why Salmonella levels rema