Evaluation of thymol-ß-D-glucopyranoside as a potential prebiotic intervention to reduce carriage of zoonotic pathogens in weaned and feeder pigs

Authors: GIZEM, LEVENT - Texas A&M University; Anderson, Robin; PETRUJKIC, BRANKO - University Of Belgrade; Poole, Toni; He, Louis; Genovese, Kenneth - Ken; Hume, Michael; Beier, Ross; Harvey, Roger; Nisbet, David

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2021
Publication Date: 4/16/2021
Citation: Gizem, L., Anderson, R.C., Petrujkic, B., Poole, T.L., He, L.H., Genovese, K.J., Hume, M.E., Beier, R.C., Harvey, R.B., Nisbet, D.J. 2021. Evaluation of thymol-ß-D-glucopyranoside as a potential prebiotic intervention to reduce carriage of zoonotic pathogens in weaned and feeder pigs. Microorganisms. 9(4). Article 860. https://doi.org/10.3390/microorganisms9040860.
DOI: https://doi.org/10.3390/microorganisms9040860

Interpretive Summary: The gut of food-producing animals can be a reservoir for human foodborne disease-causing bacteria. Strategies are sought to reduce the carriage of these bad bacteria in animals before they arrive at the processing plant, thereby contributing in a multi-hurdle farm-to-fork food safety control strategy. Thymol is a natural compound found in spices made from plants that has been shown to effectively kill these bad bacteria when studied on the laboratory benchtop but, because it is rapidly absorbed in the stomach when fed to animals, it is not able to get to the large intestine where the bad bacteria primarily reside. To try and overcome this limitation, we tested a chemical precursor of thymol that is larger in size and more resistant to being absorbed in the stomach, thereby being more likely to pass through the animal gastrointestinal tract to arrive to the large intestine where enzymes by beneficial bacteria in the large intestina can transform the thymol-precursor into free thymol. This adjustment will make it available to kill the bad bacteria. Results from the live animal studies with pigs were not successful in achieving reductions in large intestinal concentrations of the bad bacteria possibly because degradation and absorption of the thymol-precursor was still absorbed too fast in the stomach. Comparison of antimicrobial resistance profiles of the bad bacteria indicated that exposure of these bad bacteria to the thymol-precursor or thymol did not cause the bacteria to be resistant to thymol or other antimicrobials. Additional research is currently underway to try and learn how to overcome obstacles preventing delivery of thymol to the large intestine. This research provides valuable information that can help researchers ultimately provide new technologies that will be able to affordably and effectively reduce the carriage of foodborne pathogens in animals and the foods they produce, thereby decreasing the risks of food poisoning among American consumers of meat and milk.

Technical Abstract: The gut of food-producing animals is a reservoir for human foodborne pathogens. Thymol is bactericidal against pathogens including Campylobacter, Escherichia coli, and Salmonella, but its rapid absorption from the proximal gut reveals a need for protective technologies to deliver effective concentrations to the lower gut where the pathogens mainly colonize. Because of its ß-glycosidic bond, thymol-ß-D-glucopyranoside is more resistant to absorption than free thymol in everted jejunal segments and thus, we hypothesized it could potentially function as a prebiotic by being resistant to degradation and absorption in the proximal gut but hydrolysable by microbial beta-glycoside-hydrolyzing enzymes in the distal gut. This study was conducted to examine if oral administration of thymol-ß-D-glucopyranoside could effectively reduce intestinal carriage of indigenous Campylobacter, E. coli, and experimentally inoculated Salmonella Typhimurium in the cecum and rectum of swine. Results from live animal studies were not successful in achieving consequential reductions in cecal and rectal concentrations of Campylobacter, E. coli, or Salmonella, possibly because hydrolysis and absorption of thymol-ß-D-glucopyranoside and free thymol may still be sufficiently rapid within the proximal small intestine to preclude their delivery to the cecum and large intestine. Additionally, it is also possible that uptake and internal compartmentalization of thymol-ß-D-glucopyranoside by gut bacteria, or its lipophilicity, may sequester the thymol-ß-D-glucopyranoside away from hydrolytic enzymes thus preventing the release of free thymol. Comparison of antimicrobial resistance profiles between E. coli isolates or multidrug resistant Salmonella strains did not support a hypothesis that exposure to thymol-ß-D-glucopyranoside or thymol may co-select for antimicrobial resistance. Additional research is currently underway to try and learn how to overcome obstacles preventing delivery of efficacious amounts of thymol-ß-D-glucopyranoside to the lower gastrointestinal tract.