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Technologies included ambient temperature anaerobic digester, solid separation constructed wetland, up-flow biofiltration, multi-step biological and chemical, and high-solids anaerobic digester (HSAD) treatment systems, as well as a traditional lagoon treatment system on a conventional swine-production farm. Solid and liquid samples were aseptically collected in sterile plastic bottles. Following collection, all samples were stored on ice in a transport cooler and processed in the laboratory within 2 hours. Twenty-five-gram solid samples and 25-mL liquid samples were used to determine Salmonella presence and most probable number (MPN) population estimates using culture methods.
Fifty Salmonella isolates were successfully serotyped, originating from the ambient temperature anaerobic digester treatment system (four), the constructed wetland treatment system (nine), the up-flow biofiltration treatment system (18), the multi-step biological and chemical treatment system (12), the HSAD treatment system (two), and the conventional swine operation unit (five). The antimicrobial susceptibilities of the 50 serotyped Salmonella isolates were determined.
Salmonella populations in the final treated liquid waste streams of the ambient temperature anaerobic digester, constructed wetland, and multi-step biological and chemical treatment systems were under the detection limit (1 log MPN per mL), while in the final treated liquid wastes of the HSAD and the up-flow biofiltration treatment systems, populations were above the detection limit. Salmonella populations in the separated solids wastes from the constructed wetland, multi-step biological and chemical, and up-flow biofiltration treatment systems were also above the detection limit (1 log MPN per g). For each treatment technology, Salmonella populations from fresh swine feces were either low or below the detection limit.
A total of nine serotypes were identified, including Salmonella Derby (15 of 50 isolates, 30%), Salmonella Typhimurium (var Copenhagen, 12 of 50, 24%), Salmonella Johannesburg (8 of 50, 16%), Salmonella Anatum (5 of 50, 10%), Salmonella Infantis (3 of 50, 6%), Salmonella Muenchen (3 of 50, 6%), Salmonella Senftenberg (2 of 50, 4%), Salmonella Heidelberg (1 of 50, 2%) and Salmonella Worthington (1 of 50, 2%). The antimicrobial agents to which Salmonella isolates (n = 50) were most commonly resistant were tetracycline (29 of 50 isolates, 58%), streptomycin (28 of 50, 56%), ampicillin (10 of 50, 20%), chloramphenicol (6 of 50, 12%), trimethoprim-sulfamethoxazole (3 of 50, 6%), and kanamycin (3 of 50, 6%). Sixty-eight percent of the isolates were resistant to ≥ 1 antimicrobial agent. No Salmonella isolates were resistant to amikacin, amoxicillin-clavulanic acid, cefoxitin, ceftriaxone, ceftiofur, ciprofloxacin, gentamicin, nalidixic acid, or sulfisoxazole.
Most treatment technologies showed potential in reducing Salmonella populations in treated liquid manure. The technologies surveyed appear promising for reducing swine-manure Salmonella populations. Further study over an extended time frame is warranted prior to drawing any conclusions about the efficacy of these waste-treatment technologies in reducing Salmonella populations.
Payne JB, Li X, Santos FBO, et al. Survey of Salmonella populations from swine waste-treatment technologies. J Swine Health Prod. 2011;19(2):100–106.
