Drinking Water Supplementation of trans-Cinnamaldehyde-Miglyol Microemulsions Reduces Multidrug-Resistant Salmonella Heidelberg in Turkey Poults and Augments the Antibacterial Effect of Oxytetracycline

The use of clinically important antibiotics in U.S. poultry production has decreased drastically over the past decade. They can only be used to treat diseases under the supervision of a veterinarian. Reducing antibiotic use, even for disease treatment, can improve the long-term sustainability of the industry. In the current study, we examined the effect of supplementation of a low dose of <i>trans</i>-cinnamaldehyde (<b>TC</b>; 0.03%), a GRAS-status plant-derived compound, with or without oxytetracycline (<b>OTC</b>; 16 μg/mL), an anti-30S ribosomal subunit targeting antibiotic, on the multidrug-resistant (<b>MDR</b>) <i>S.</i> Heidelberg (<b>SH</b>) in turkey poults. Two independent experiments were conducted (N = 96). In each experiment, 48, straight-run, day-old, commercial Hybrid Converter turkey poults were randomly assigned to 6 treatments of 8 birds each: Negative Control [<b>NC</b>; -SH, -TC, -OTC, -0.06% Miglyol (<b>MIG</b>, emulsifier for TC in water)], Positive Control (<b>PC</b>; +SH, -TC, -OTC, -MIG), MIG Control (MIG; +SH, -TC, -OTC, +MIG), TC Group (<b>TC</b>; +SH, +TC, -OTC, +MIG), OTC group (<b>OTC</b>; +SH, -TC, +OTC, -MIG), and TC+OTC group (<b>TC+OTC</b>; +SH, +TC, +OTC, +MIG). OTC was supplemented from day 1 through drinking water throughout the experiment. The birds in the TC and TC+OTC groups were supplemented with TC in their drinking water for 7 days post-challenge. All birds were challenged on day 7 with 6 log₁₀ CFU of SH/bird via crop gavage. On day 14, all birds were euthanized to collect the cecum, liver, and spleen for pathogen recovery. TC at 0.03% emulsified in MIG was highly effective in reducing MDR SH colonization in turkey poults (<i>p</i> < 0.05) compared to the SH control (>4.5 log₁₀ CFU/g reduction) on day 14. The OTC group reduced the pathogen load by 2.5 log₁₀ CFU/g by day 14. TC enhanced the effect of OTC, reducing pathogen load by ~3.9 log₁₀ CFU/g compared to the SH control after 7 days. TC significantly reduced SH invasion into the liver and spleen compared with the SH control on day 14. The results of the study indicate that TC at 0.03% can augment OTC at 16 μg/mL for the treatment of MDR SH infection in poults and could be an industry-sustainable strategy.