Use of Rainfall Simulation to Determine the Persistence and Transport of Escherichia coli and Salmonella in Runoff Water

Manure applied to cropland to increase its productivity may harbor pathogenic bacteria such as Salmonella and E. coli O157:H7. Runoff water simulated by heavy rainfalls may carry these bacteria to nearby water bodies that are used to irrigate fresh produce; causing human illnesses once these vegetables are consumed. This study examined the persistence of E. coli, E. coli O157:H7 and Salmonella in runoff water yielded from soil amended with different types of animal manure. Four rainfall events were conducted where soil was packed in stainless runoff boxes, 20 cm long, 29 cm wide and 5 cm deep with back walls 2.5 cm higher than the soil surface, and 5 mm drainage hole in the base. Soil was amended with poultry litter, poultry litter incorporated, broiler manure, dairy manure, or ammonium sulfate as a control, and each treatment was replicated five times. Runoff water was collected from each box to determine the concentrations of the target bacteria using IDEXX Quanti-Trays TM/2000. Water samples were also incubated in the Quanti-Trays at 35° C for 18–24 hours where Most Probable Number (MPN) for each sample was determined. Water samples were also spiral plated onto Xylose- Lysine-Tergitol 4 (XLT4) and MacConkey sorbitol agar (CTSMAC) to detect for the presence of E. coli O157:H7 and Salmonella.  Furthermore, BAX PCR was used to confirm the presence of these bacteria in water samples; however, this test failed to confirm the presence of Salmonella and E. coli O157:H7. Results showed that the population of E. coli was declined by 98.2%, 99.9&, and 94.3% in soils amended with incorporated, and broadcasted poultry litter, and dairy manure respectively.  In general, there was no significant difference in E. coli concentrations among the types of manure.