Managing Salmonella Typhimurium and Escherichia coli O157:H7 in soil with hydrated lime – An outdoor study in lysimeters and field plots

Abstract

An outbreak of Salmonella Typhimurium or E. coli O157:H7 among domestic animals can have great financial consequences for an animal enterprise but also be a threat for public health as there is a risk for transmission of the infection through the environment. In order to minimize disease transmission, it is important to treat not only the affected animals but also the areas on which they have been kept. In the present study, the effect of hydrated lime as a treatment for Salmonella Typhimurium or E. coli O157:H7 contaminated soil was investigated. The study was performed outdoors, in a lysimeter system and in field plots. The soils were spiked with Salmonella Typhimurium and/or E. coli O157:H7 and hydrated lime was added at three different concentrations (0.5, 1 and 2%). Sampling was performed over one month, and the levels of bacteria were analyzed by standard culture methods. In addition, the soil pH was monitored throughout the study. The results showed that application of 0.5–1 kg hydrated lime per m² reduced both Salmonella Typhimurium and E. coli O157:H7 numbers to below the detection limit (2 log10 CFU g-1 soil) in 3–7 days. Lower application rates of hydrated lime did not reduce pathogen numbers in the lysimeter study, but in the field plots no E. coli O157:H7 was detected at the end of the four-week study period regardless of hydrated lime application. A recommended strategy for treating a Salmonella Typhimurium or E. coli O157:H7 contaminated soil could therefore be to monitor the pH over the time of treatment and to repeat hydrated lime application if a decrease in pH is observed.

Keywords:

• Treatment
• microbial contamination
• pathogen
• environment

Acknowledgments

We wish to acknowledge Emelie Kjellberg for assistance with the laboratory work, Richard Childs for assistance with soil collection and lysimeter installation and Tomas Rydberg for support during field trial set-up. The project was funded by the Swedish-Norwegian Foundation for Equine Research and the Swedish Civil Contingencies Agency (MSB).