Food producing animals can be reservoirs of Campylobacter, a leading bacterial cause of human foodborne illness. Campylobacter spp. utilize amino acids as major carbon and energy substrates, a process that can be inhibited by thymol and diphenyliodonium chloride (DIC). To determine the effect of these potential additives on feed intake, live weight gain, and gut Campylobacter levels, growing pigs were fed standard grower diets supplemented with or without 0.0067 or 0.0201% thymol or 0.00014 or 0.00042% DIC in a replicated study design. Diets were offered twice daily for 7 days, during which time daily feed intake (mean ± SEM, 2.39 ± 0.06 kg day−1) and daily gain (0.62 ± 0.04 kg day−1) were unaffected (P > 0.05) by treatment. Pigs treated with DIC but not thymol tended to have lower rectal Campylobacter levels (P = 0.07) (5.2 versus 4.2 and 4.4 log CFU g−1 rectal contents for controls and 0.00014% DIC and 0.00042% DIC, respectively; SEM = 0.26). However, DIC or thymol treatments did not affect (P > 0.05) ileal or cecal Campylobacter (1.6 ± 0.17 and 4.5 ± 0.26 log CFU g−1, respectively), cecal total culturable anaerobes (9.8 ± 0.10 log CFU g−1), or accumulations of major fermentation end products within collected gut contents. These results suggest that thymol and DIC were appreciably absorbed, degraded, or otherwise made unavailable in the proximal alimentary tract and that encapsulation technologies will likely be needed to deliver effective concentrations of these compounds to the lower gut to achieve in vivo reductions of Campylobacter.

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Author notes

Mention of trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable.

Results of this study were presented in preliminary form at the 8th International Symposium on the Epidemiology and Control of Foodborne Pathogens in Pork in Quebec City, Canada, 30 September to 2 October 2009.

§ Present address: 32-056 Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, 450 West Drive, Chapel Hill, NC 27599-7295, USA.