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  5. The Use of Probiotic Megasphaera elsdenii as a Pre-Harvest Intervention to Reduce Salmonella in Finishing Beef Cattle: An in vitro Model
Project Summary

The Use of Probiotic Megasphaera elsdenii as a Pre-Harvest Intervention to Reduce Salmonella in Finishing Beef Cattle: An in vitro Model 

Principle Investigator(s):
Kellen Habib, James Drouillard, Vanessa Veloso, Valentina Trinetta, Sara E. Gragg
Institution(s):
Department of Animal Sciences and Industry, Kansas State University
Completion Date:
January 2022

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KEY TAKEAWAYS

  • Treating ruminal fluid with Megasphaera elsdenii (ME) did not significantly impact Salmonella populations or volatile fatty acid production. The pH of ruminal fluid and feces decreased over time. 
  • Salmonella populations declined in feces, with the largest reduction in antibiotic susceptible Salmonella by the 2.5 x 105 CFU/g concentration of ME; however, a 1.05 log MPN/g reduction was also observed for control feces inoculated with antibiotic susceptible Salmonella between 0 and 72 hours.
  • Treating ruminal fluid with ME did not impact Salmonella populations. Salmonella populations in feces may be decreased by treatment with ME, but decreases observed were marginal, and ME must be further investigated before a conclusion regarding efficacy can be determined.

BACKGROUND

Cattle naturally harbor Salmonella in their gastrointestinal tract (GI tract), lymph nodes, and feces. The potential transmission of Salmonella to humans from cattle is a public health risk. Reducing Salmonella carriage in the GI tract of cattle may be one important way to mitigate the risk of Salmonella transmission through food. Megasphaera elsdenii (ME) is a microorganism naturally found in the rumen of cattle that is often administered to as a probiotic to reduce ruminal acidosis. The use of ME as a probiotic to also reduce Salmonella shedding in cattle has not been explored and warrants investigation.


Methodology   
Ruminal fluid and feces were obtained from cattle and inoculated with antibiotic susceptible or resistant Salmonella. Ruminal fluid and feces not inoculated were also prepared for testing naturally occurring Salmonella populations, volatile fatty acids (VFAs), and pH. ME was prepared at varying concentrations and used to treat the inoculated and non-inoculated ruminal fluid and fecal samples. Samples were stored under anaerobic conditions on a shaking incubator set at 38.6oC and 50RPM to simulate a bovine’s body temperature and peristaltic GI tract motion, respectively. Samples were enumerated for Salmonella using most probable number (MPN) at 0, 24, 48, and 72 hours. VFAs and pH were determined at each sampling point using the non-inoculated samples.

Findings   
Salmonella populations (antibiotic susceptible and resistant) and VFAs in ruminal fluid were not significantly impacted by treatment with ME (P>0.05). The pH of ruminal fluid and feces decreased over time (P<0.05). The largest decline in Salmonella populations in feces occurred between 0 and 72 hours, with 1.92 log MPN/g reduction observed in antibiotic susceptible Salmonella populations by the 2.5x105 CFU/g ME concentration. However, a 1.05 log MPN/g reduction was also observed between 0 and 72 hours for control feces inoculation with antibiotic susceptible Salmonella. Antibiotic susceptible and resistant Salmonella populations in ruminal fluid were not impacted by the addition of ME at any concentration. Fecal Salmonella populations may be reduced by ME treatment with ME; however, only marginal reductions were achieved in comparison to control feces. Additional research is necessary before the efficacy of ME at reducing Salmonella populations in cattle can be determined.

Implications 
The use of ME as a probiotic to mitigate ruminal acidosis is important for the industry. In terms of feasibility and maximal cost:benefit ratio, it would be advantageous if ME also provided a food safety benefit by reducing Salmonella populations in ruminal fluid and/or feces. The use of this in vitro model provides preliminary evidence that ME provides no protection against Salmonella in ruminal fluid and marginal protection, at best, against Salmonella in feces. There are challenges associated with an in vitro model in terms of accurate simulation of the gastrointestinal tract of cattle. This approach provides preliminary data that 1) cannot lead to the conclusion of efficacy, but 2) may warrant additional research in the live animal where anaerobic conditions can be maintained and there is a regular infusion of nutrients as the animal eats. While ME cannot be recommended at this point as a food safety intervention to reduce Salmonella in cattle, the opportunity exists for Salmonella to be detected and enumerated from the feces of cattle supplemented with ME in a feedlot setting as the next step in investigating the efficacy of this microorganism as a probiotic.