Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 15, 2008
Publication Date: April 1, 2008
Citation: Wells, J., Varel, V.H. 2008. Viability of zoonotic pathogens Escherichia coli and Salmonella in swine manure slurries with and without a urease inhibitor and thymol. Letters in Applied Microbiology 46:477-482. Interpretive Summary: Animal manures from production facilities are often applied to land as a fertilizer. Treatments to improve nutrient content of the manure can improve the fertilizer value. Urease inhibitors offer the potential to increase nitrogen content in animal manures. However, urease hydrolysis generates compounds that reduce bacterial pathogens in the manure. As a consequence, inhibition of this hydrolysis may prolong pathogen presence. Treatments with essential oils can decrease bacterial pathogens in manures. The combination of an essential oil with the urease inhibitor was also effective at decreasing pathogens in swine manures. Manure management strategies that preserve urea nitrogen should also consider effects on manure pathogens. This may require additional treatments to prevent transmission of the pathogens into the environment as indicated in this study.
Technical Abstract: Aims: To determine the effects of urine, a urease inhibitor and/or an odor-reducing compound, on zoonotic pathogens in swine manure slurries. Methods and Results: Swine faeces were collected and blended with different amounts of urine. Marker strains of Salmonella enterica Typhimurium and Escherichia coli O157:H7 were inoculated into the manure slurries with or without the urease inhibitor, N-(n-butyl) thiophosphoric triamide (NBPT), or the odor-reducing compound thymol. In slurries containing approximately 1:1 or 2:1 of urine and faeces, the decrease in viability of Salmonella and E. coli were similar and few viable cells were found after 14 days. When the urine content of the slurry was increased to 5:1, both strains died off rapidly. When NBPT was added to the slurries, pathogen viability was not affected in the 1:1 slurry. The 2:1 and 5:1 slurries had higher urea content and NBPT increased survival of both pathogens. Thymol addition rapidly killed the pathogens and few viable counts of Salmonella or E. coli were observed after day one. Conclusions: These experiments demonstrate that urea hydrolysis in swine manure affects pathogens. Inhibition of urea hydrolysis may promote pathogen viability. Significance and Impact of the Study: Manure amendments that prevent urea hydrolysis may promote pathogen viability. Additional treatments with antimicrobials may be required to kill pathogens.