Purpose: A two-year study was performed to investigate the diversity and dynamics of Salmonella enterica spp. in irrigation water and poultry litter amended fields on the eastern shore of Virginia.
Methods: Irrigation pond water and well water were sampled weekly from four vegetable farms (farm A-D) in 2014 and 2015. Soil samples were collected monthly after fertilization with chicken manure from 10 farms in 2014, and another 14 farms in 2015. The most probable number (MPN) method was used to quantify Salmonella spp. in the samples. Presumptive Salmonella colonies were confirmed by the cross-streaking method. Molecular serotyping was carried out to determine Salmonella serovars.
Results: The observed prevalence of Salmonella in pond irrigation water was approximately the same in 2014 (19.9%) and 2015 (19.4%), while the average concentration in the water increased from 0.49±1.66 MPN/L in 2014 to 0.82±5.14 MPN/L in 2015. All wells were Salmonella positive except from farm B at certain time points, especially in farm D. The prevalence (<4%) of Salmonella in Well water was significantly lower than that for Pond water (P<0.01), and had an average level value of 0.03±0.15 MPN/L in 2014 and 0.05±0.36 MPN/L in 2015. Salmonella was found to be able to survive up to four months in poultry litter amended soils from the tested farms in 2014, and up to six months in 2015. There were spatial and temporal differences for Salmonella serovar diversity in water and soil samples.
Significance: This research examined the dynamics of Salmonella spp. in relationship to irrigation water sources and poultry litter used for vegetable production, and provides useful information for food safety risk assessment.