Purpose: To investigate the survival of Salmonella spp. in fields amended with poultry litter, and in artificially inoculated soil in a growth chamber.
Methods: In field experiments, naturally contaminated poultry litter with Salmonella (700 MPN/kg) was collected and amended into soil to emulate manure fertilization at four levels of 0 kg (control), 5 kg, 25 kg, and 100 kg per plot (45 m2). Soil samples were tested monthly for Salmonella contamination by the MPN method for nine months. In a laboratory experiment, a Salmonella cocktail inoculum of five serovars was mixed into soils collected from tomato fields to reach initial concentrations of 2, 4 and 6 log CFU/g. Salmonella populations after treatment were determined daily in the first week, and weekly for next three months. A randomized block design with four replications was performed in both field and laboratory experiments.
Results: In field experiments, Salmonella was isolated from plots that had received 25 kg of poultry litter in month 1 with an average population density of 12 MPN/kg (95% CI: 5.4 to 25 MPN/kg). Plots treated with 100 kg poultry litter were found positive for Salmonella four months after soil amendment with initial concentration of 14 MPN/kg (95% CI: 6.8 to 28 MPN/kg). No Salmonella was isolated from the 5 kg treatment or control plots during the study. In laboratory experiments, Salmonella populations decreased in inoculated soils over the testing period. The pathogen was no longer detected after 5, 7, and 9 weeks after inoculation with initial concentration of 2, 4 and 6 log CFU/g, respectively.
Significance: Data derived from the study can be used in risk assessments to determine the public health implications of using raw manure as a soil amendment.