Author: Casas Murillo, Diego Eduardo 0000-0002-7897-9904

According to the World Bank, foodborne illness costs over $110 billion per year in low- and middle-income countries. In the United States, Salmonella and big 7 Shiga toxin-producing E. coli (STEC) account for 26% of economic burden of foodborne illness. Meat and poultry are attributed approximately 38% and 27% of Salmonella and E. coli O157:H7 foodborne illnesses respectively. Consequently, the beef industry has diligently developed and researched different antimicrobial mitigation strategies that will reduce the concentration and prevalence of Salmonella and E. coli O157:H7, as well as antibiotic resistance development throughout the beef production chain. In our first study, the objective was to determine the effect of dietary L28 and tylosin on Salmonella, Enterococci, generic E. coli, and E. coli O157 presence in fecal grabs, perineal and hide swabs, and subiliac lymph node samples and their antimicrobial susceptibility profile. Generic E. coli and Enterococci presence were high throughout the feeding trial, 98.3% and 96.1% respectively. Salmonella presence was substantially high (62.7%) within pens and similar among treatments. No effects (P > 0.152) among treatment on microbial presence were observed in any of the four microorganisms studied within the pen and perineal samples. However, Salmonella presence within lymph nodes was affected by the treatments (P < 0.001). The MONPRO treatment (34.8%, 26/46) had a greater presence of Salmonella than the MONTY (8.7%, 4/46) and the PRO treatment (0.0%, 0/42). The presence of Salmonella, Enterococci, generic E. coli, and O157 did not increase with supplementation of L28 compared to the control. All Salmonella isolated was susceptible to every antibiotic class evaluated except one isolated with ample resistance to β-lactams. No significant difference (P > 0.05) between treatments was observed in the overall phenotypic resistance of Salmonella, E. coli, and Enterococci. Moreover, a tendency in the increase of overall resistance was observed across treatments as the days of feed increased. The absence of Salmonella in L28 treatment lymph nodes suggests supplementation of L28 may contribute to mitigating Salmonella’s capacity to invade the lymphatic system. This poses a significant contribution to the beef industry as lymph nodes can be a substantial source of Salmonella in ground beef. In the second study the objective was to conduct a longitudinal field study to probe the impact of the soil properties and weather on Salmonella survival and persistence in the feedlot ecosystem. Subsequently leading to the identification of factors that can be used as pre-harvest mitigation strategies. Salmonella prevalence varied throughout the seasons (P < 0.01), where the highest prevalence was observed in summer and fall seasons. A difference in prevalence between feedlots was observed (P <0.01), Feedlot 4 had the highest prevalence with an average of 57.2% (151/264) in all the year. In comparison, Feedlot 3 had a 17.4% (46/264) average prevalence in the year. Surface pen samples had a higher presence of Salmonella than deeper soil stratum sampled. Soil nutrient profile exploratory analysis showed a significant predictor effect in Salmonella presence, suggesting potassium, phosphorus, and calcium concentration in soil were positively correlated with Salmonella presence, whereas copper and magnesium were negatively correlated with Salmonella presence. Further research will elucidate the effect specific nutrients in the soil have on Salmonella presence and persistence. Moreover, seasonal variation of Salmonella presence can lead to tailored interventions at different stages of the year based on the possible risk of Salmonella entrance into the beef processing environment and have a risk-based approach to Salmonella mitigation to further ensure food safety. In the third study, the objective was to evaluate the antimicrobial efficacy of an aqueous ozone (Bio-Safe) treatment and lactic acid solutions on natural microbiota and E. coli O157:H7 and Salmonella surrogates on beef carcasses and trim in a commercial beef processing plant. Ozone and lactic acid interventions significantly reduced (p < 0.003) bacterial counts in carcasses and trim samples. Moreover, lactic acid further reduced APC and coliforms in trim samples compared to ozone intervention (p < 0.009). In the surrogate trials, ozone significantly reduced (p < 0.001) surrogate concentration. Historical data from the plant revealed a reduction (p < 0.001) of presumptive E. coli O157:H7 in trim after a full year of ozone intervention implementation. The novel technology for ozone generation and application as an antimicrobial can become an alternative option that may also act synergistically with existing interventions, minimizing the risk of pathogens such as Salmonella and E. coli O157:H7. In the fourth study, the objective was to determine the impact of spray and dry chilling combined with hot water carcass treatments on the levels of microbial indicator organisms during the long-term refrigerated storage of beef cuts. Not enough evidence (p > 0.05) was found indicating the hot water wash intervention reduced bacterial concentration on the carcass surface. E. coli was below detection limits (< 0.25 CFU/cm2) in most of the samples taken. No significant difference (p > 0.05) was found between coliform counts throughout the sampling dates. Feed type did not seem to influence the (P > 0.25) microbial load of the treatments. Even though no immediate effect was seen when comparing spray or dry chilling of the samples at day 0, as the product aged, a significantly lower (p < 0.05) concentration of aerobic and psychrotrophic organisms in dry-chilled samples could be observed when compared to their spray-chilled counterparts. Data collected can be used to select alternative chilling systems to maximize shelf life in vacuum packaged beef kept over prolonged storage periods.