Salmonella and E. Coli O157:H7 Transport and Retention in Intact and Disturbed Soil Columns.

In order to devise methods to suppress and control zoonotic pathogenic bacteria threatening human and animal health, it is important to understand their behavior in the agroecosystem.  A leaching column study was initiated to study transport through and retention in the soil profile of the pathogens Salmonella enterica serovar Newport and fluorescent protein-labeled E. coli O157:H7.  Soil columns of 10 cm diameter and 15 cm depth were collected from the field.  Soil variables were 1) undisturbed cores with sod cover vs. tilled, or silt loam vs. sandy loam texture.  Pathogens were inoculated into dairy manure at a target rate of 7 log 10 per gram and applied to the surfaces of the cores.  Simulated rainfall was applied periodically over 14 days with three different application patterns.  Leachate samples, soil increments and manure samples were collected and enumerated for concentrations of Salmonella and pathogenic E. coli.  There were significant differences in pathogen leaching and soil retention behavior as a function of both tillage and soil texture.  Over all simulated rainfall patterns, Salmonella losses in leachate were not different from those of E. coli O157:H7 in the silt loam soil while E. coli O157:H7 exceeded Salmonella in the sandy loam.  Conversely, soil retention of Salmonella was significantly greater than E. coli in the silt loam soil but not different in the sandy loam.  For E. coli, leaching losses and soil retention were significantly greater in undisturbed than tilled silt loam cores, but similar for Salmonella.  Differential adhesion to soil aggregates and movement through natural soil water flow pathways likely contribute to behavior in the soil system of the two common enteric pathogens.