Effect of chemostat turnover rate and select antibiotics on Salmonella Typhimurium in the presence of porcine gastrointestinal tract bacteria

Authors: Anderson, Robin; Poole, Toni; Crippen, Tawni - Tc; Harvey, Roger; RICKE, STEPHEN - University Of Wisconsin

Submitted to: Canadian Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2023
Publication Date: 10/16/2023
Citation: Anderson, R.C., Poole, T.L., Crippen, T.L., Harvey, R.B., Ricke, S.C. 2023. Effect of chemostat turnover rate and select antibiotics on Salmonella Typhimurium in the presence of porcine gastrointestinal tract bacteria. Canadian Journal of Animal Science. 104(1):118–122. https://doi.org/10.1139/cjas-2023-0019.
DOI: https://doi.org/10.1139/cjas-2023-0019

Interpretive Summary: Concern exists that the use of antibiotics in animal feeds may lead to an increase of antimicrobial resistant bacteria within the host animal's gut. In order to evaluate the effect of select antibiotics on the persistence of an antibiotic resistant foodborne bacterial pathogen Salmonella typhimurium, we grew Salmonella typhimurium within a diverse population of porcine gut bacteria in a laboratory simulation of the pig gut. During growth in the presence of the antibiotics: bacitracin, oxytetracycline, and tetracycline, the test Salmonella typhimurium, despite being inherently resistant to these antibiotics, decreased to undetectable levels by 8 days of culture in the simulated gut model. This is likely because many of the beneficial bacteria in the gut were also resistant to these antibiotics. Modifying the cultural conditions to increase the competitiveness of the antibiotic resistant Salmonella typhimurium over the beneficial microbes, by simulating an increased gut emptying rate or by adding another antibiotic, carbadox, promoted retention of the antibiotic resistant Salmonella typhimurium at higher levels and for longer time periods. This suggests that treatments administered in this gut model successfully inhibited the resident population of beneficial microbiota, thereby curtailing their ability to competitively exclude the Salmonella typhimurium as would be expected in the animal. The use of gut models such as the one used here may provide new insight into the complex interactions that can occur between pathogenic and beneficial microbes, thereby helping livestock producers safely and effectively manage the use of antibiotics to ensure the production of wholesome and safe pork for the American consumer.

Technical Abstract: The effect of select antibiotics on Salmonella Typhimurium DT104 persistence in a porcine cecal continuous flow culture was examined under two different washout rates. Porcine continuous flow cultures were conducted in the presence or absence of Gram-positive antibiotic carbadox. Carbadox eliminated chemostat anaerobes culturable on Brucella agar under 24 h turnover conditions, allowing Salmonella Typhimurium to persist for 15 days. Decreasing the culture dilution rate from a 24 to 48 h turnover time enabled Salmonella Typhimurium to maintain higher population levelsmore reflective of the theoretical washout rate when grown with than without added carbadox. This observation suggests that at the slower growth rate the presence of carbadox was antagonistic to the indigenous competitive exclusion potential of the mixed microbial population.