Abstract
The Eastern Shore of Virginia (ESV) is a major agricultural region in Virginia and in the past has been linked to some tomato-associated outbreaks of salmonellosis. In this study, water samples were collected weekly from irrigation ponds and wells in four representative vegetable farms (Farms A–D, each farm paired with one pond and one well) and a creek as well. In addition, water samples from two sites in the Chesapeake Bay on the ESV were collected monthly. Poultry litter was sampled monthly from three commercial broiler farms. Soil samples were collected monthly after fertilization with poultry litter from 10 farms in 2014 and another 14 farms in 2015. A most probable number method was used to detect Salmonella enterica presence and concentration in collected samples. Presumptive Salmonella colonies were confirmed by the cross-streaking method. Molecular serotyping was carried out to determine the Salmonella serovars. The average prevalence of Salmonella in pond, well, creek, and bay water samples was 19.3, 3.3, 24.2, and 29.2%, respectively. There were significant spatial and temporal differences for Salmonella incidence in various water sources. The prevalence of S. enterica in four tested ponds from farms A, B, C, and D were 16, 12, 22, and 27%, respectively. While the prevalence of S. enterica in irrigation wells was significantly lower, some well water samples tested positive during the study. Salmonella Newport was found to be the predominant serovar isolated from water samples. All poultry houses of the three tested broiler farms were Salmonella-positive at certain sampling points during the study with prevalence ranging from 14.3 to 35.4%. Salmonella was found to be able to survive up to 4 months in poultry litter amended soils from the tested farms in 2014, and up to 6 months in 2015. This research examined the dynamics of S. enterica in relationship to water source, poultry litter, and amended soil in a major agricultural area, and provides useful information for food safety risk assessments.
Highlights
MATERIALS AND METHODSSalmonella is the most frequently encountered bacterial pathogen associated with foodborne illness in the United States [Food Safety News (FSN), 2011; Centers for Disease Control and Prevention, 2019]
The same pulsed field gel electrophoresis (PFGE) type Salmonella Newport was associated with the 2014 outbreak associated with cucumber, which was determined to have originated from the Eastern Shore of Maryland (Angelo et al, 2015)
Salmonella was detected in water samples from all four ponds at varying times during the course of the study [19.25% positive samples (n = 400); average population density: 0.63 ± 0.02 most probable number (MPN)/L]
Summary
Salmonella is the most frequently encountered bacterial pathogen associated with foodborne illness in the United States [Food Safety News (FSN), 2011; Centers for Disease Control and Prevention, 2019]. The prevalence and serovar diversity of S. enterica were investigated in various water sources (creek, well, bay), broiler farms (raw poultry litter), and poultry litter amended soils (in agricultural fields). Farms tested in this study for irrigation water, poultry litter, and soil sampling were independently operated and geographically distinct (distance >3 km). The same test was performed to evaluate the difference of Salmonella prevalence between the two sampling sites of the Chesapeake Bay. GLIMMIX analysis was conducted to evaluate the effect of broiler farm location and poultry litter type (wet and dry) on Salmonella prevalence and population density. The same analysis was performed to assess the difference of Salmonella population density among the sample types (water, poultry litter, and soil) tested in this study. Values of p < 0.05 were considered statistically significant
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