PS4-9. Characterization of Feed-borne Microbes and Establishment of a Salmonella Contamination Model

Feed is recognized as a potential vehicle for delivering pathogens including Escherichia coli and Salmonella spp., to livestock. From a One Health perspective, increasing regulatory and consumer pressure exists to identify effective alternatives to formaldehyde-based feed sanitizers in swine and poultry production. However, suitable models to evaluate the efficacy of such alternatives in feed are limited. This study aimed to investigate feedborne bacterial contamination and to develop a Salmonella feed contamination model. Different batches of ingredients of animal protein–based feed and vegetarian feed were collected in a feedmill, and their E. coli and Salmonella spp. loads were analyzed. Agar plating was used to quantify bacteria, and DNA extracted from feedborne E. coli was screened for antibiotic resistance genes (TET, ermK, MarB, and BlaTem) and pathogenicity genes (FIM, STX2, and eae) using real-time qPCR and agarose gel electrophoresis. E. coli was detected in corn (4.67 log10 CFU/g), SBM (3.81), DDGS (4.83), animal protein feed (5.03), and vegetarian feed (4.67), but was absent in vitamin-mineral premixes, calcium and phosphorus sources, and protein supplements including fish meal, plasma protein, and whey isolate. Salmonella was not detected in any feed ingredient. Antibiotic resistance genes (TET, ermK, MarB, and BlaTem) and FIM were present in both animal and vegetarian diets, while STX2 was detected in 2 of 6 vegetarian diets and absent in animal diets. The eae gene was absent in all vegetarian diets but was detected in 3 of 6 animal diet batches. Using this data, a Salmonella Typhimurium contamination model was established by inoculating SBM with an overnight culture (9 log10 CFU/g, ampicillin-resistant strain in fresh TSB; 1% per feed, 2 mL per 200 g feed), followed by the addition of other vegetable ingredients. Salmonella was successfully inoculated, achieving high initial counts (D0: 5.8 log10 CFU/g), which gradually declined over time (D2: 4.8; D4: 3.7; D8: 2.92). Inclusion of 0.3% formaldehyde-based commercial feed sanitizer, positive control) significantly reduced Salmonella counts at D 0 (Negative control: 5.12 log10 CFU/g vs. Positive control: 3.93 and D 2 (Control: Negative control: 3.61 log10 CFU/g vs. Positive control: 1.31). This study provides a reliable model for evaluating potential natural alternatives to formaldehyde-based feed sanitizers in livestock feed.