Date Full Report Received


Date Abstract Report Received



Primary Investigator:

There is tremendous pressure on the US pork industry to ban the prophylactic and growth promotion use of antimicrobials in feed due to the generation of antimicrobial resistant (AMR) bacterial strains. An important concern is the dissemination of AMR Salmonella in the environment after swine manure application. The main objective of this study was to determine the potential role of lagoons and manure pits in the transmission of AMR Salmonella in the environment following land application of swine manure on commercial swine farms in Iowa (n=7) and North Carolina (n=6). In Iowa the manure is stored in pits and applied using an injection system while manure in NC is stored in lagoons and applied directly on the soil using a spray method. Salmonella prevalence was compared on these conventional swine farms at different time points including day 0 (before and after manure application) and subsequently on days 7, 14 and 28 post manure application on specific land locations at every site. The samples consisted of lagoon/manure pit and soil on day 0 while only soil samples were collected on the following sampling time points. Overall, we collected a total of 1,200 soil samples (IA=700; NC=500) and 50 lagoon and 70 manure pit samples from NC and IA, respectively. Overall Salmonella prevalence was 13.33% (176/1320) while the prevalence in soil and lagoon were 10.92% and 37.5%, respectively. The Salmonella prevalence in North Carolina (28.18%) was significantly higher than in Iowa (2.73%) (p < 0.001). We detected a significant decrease in prevalence of Salmonella from the marked areas as we moved from Day0 to Day21. We identified 12 serotypes, however, it is important to note that no serotype found in one state was detected from the other highlighting serotype association based on geographic region. For example, we detected Anatum (7.39%), Litchffield (3.98%), and Infantis (0.57%) in IA, while Altona (7.95%), Derby (3.98%), Johannesburg (3.98%), Mbandaka (1.70%), Muenster (9.09%), Rissen (0.57%), Typhimurium var5- (20.45%), Uganda (2.27%), and Worthington (5.68%) in NC. A total of 80.47% of the Salmonella isolates were multidrug resistant (MDR; resistance to three or more antimicrobials) with the most frequent AMR against Streptomycin (82.81%), sulfisoxazole (73.44%), and kanamycin (61.72%). PFGE genotyping revealed genotype relatedness among Salmonella recovered from lagoon and soil at multiple time points with relatively close geographic proximity and serotypes. Our study highlights Salmonella transmission in the environment in commercial swine farms is dependent on the type of manure storage and its application method. Finally, the rapid decline in the prevalence of Salmonella in soil samples on subsequent collection days (Days 7, 14, 21) clearly indicates the inability of this pathogen to survive in the environment for longer durations.