Interpretive Summary: Escherichia coli O157:H7 is an important foodborne pathogen that can reside in the gut of cattle. When attached to the hide or shed in the feces at slaughter this bacterium can sometimes contaminate carcasses intended to be processed for human consumption. Therefore, a need exists for new pre-harvest interventions that can prevent the carriage and excretion of this pathogen in cattle presented to the processing plant. The objectives of this study were to test the effectiveness of naturally occurring antimicrobial compounds called tannins found in chestnut or mimosa shrubs when applied as a hide-intervention and as a feed additive to feedlot cattle. We found that when applied as a spray containing 3 g of tannin compound per 100 ml of water, numbers of total coliform bacteria, measured as an indicator of E. coli O157:H7, ranged from approximately 31 to 64 cells per square centimeter of the treated hide area. However, these bacterial numbers were very similar to those measured on hides that had been sprayed with water, which indicates that at these levels the tannin solutions had little if any bactericidal activity against the measured bacteria. In a second experiment, diets supplemented without (controls) or with the different tannin compounds, added to the diet at 1.5%, were fed to cattle during a 42 day experimental feeding period. We found that numbers of total coliforms were significantly reduced in the forestomach of steers fed the chestnut-tannin compounds, with numbers averaging approximately 4,000 bacteria per gram of gut content in chestnut tannin fed steers versus an average number of approximately 12,000 bacteria in gut contents of steers fed control diets. However, the diets containing the different tannin sources did not consistently reduce numbers of total coliforms recovered in the steers’ feces, with numbers ranging from 510,000 to just over 1 million cells per gram of feces regardless of treatment or not. Similarly, we found that the tannin treatment had no reducing effect on numbers of Campylobacter, another less abundant pathogenic bacterium measured in the cattle feces, with numbers of Campylobacter ranging from 3 to 10 cells per gram of feces. These results indicate that while diets containing chestnut tannin reduced total coliforms within the forestomach of treated cattle, the antimicrobial effect was not maintained in the lower gastrointestinal tract. We conclude that further research will be necessary to determine the effective amounts and types of tannins that can be fed before these can be used by cattle feeders to reduce carriage of E. coli O157:H7. This research provides cattle producers and processors with important information on the types and quality of products being offered to help them produce safe beef products for the American consumer.
Technical Abstract: Alternative pre-harvest interventions have to be evaluated to prevent carcass contamination at the slaughter house. The objectives of this study were to examine the antimicrobial effects of hydrolysable tannin-rich chestnut and condensed tannin-rich mimosa extracts on bacterial indicators of foodborne pathogens when applied as a hide-intervention and as a feed additive to feedlot cattle. Water (control) or solutions (3% wt/vol) of chestnut- and mimosa-extract treatments were sprayed (25 ml) at the left costal side of each animal to a 1000 cm2 area, divided into four equal quadrants. Hide-swabs samples obtained at pre-, 2-min, 8-h, and 24-h post-spray application were cultured to enumerate Escherichia coli/total coliforms and total aerobic plate counts. In a second experiment, diets supplemented without (controls) or with (1.5% of diet dry matter) chestnut- or mimosa-extracts were fed during a 42 day experimental feeding period. Weekly fecal samples starting on day 0, and rumen fluid obtained on days 0, 7, 21, or 42 were cultured to enumerate E.coli/total coliforms and Campylobacter. Tannin spray application showed no effect of treatment or post-application-time (P > 0.05) on measured bacterial populations, averaging 1.7/1.8, 1.5/1.6, and 1.5/1.7 (log10 CFU/cm2) for E. coli/total coliforms, and 4.0, 3.4, and 4.2 (log10 CFU/cm2) in total aerobes for control chestnut and mimosa treatments, respectively. Mean (± SEM) ruminal E. coli and total coliform concentrations (log10 CFU/ml) were reduced (P < 0.01) in steers fed chestnut-tannins (3.6 and 3.8 ± 0.1) in comparison with the controls (4.1 and 4.2 ± 0.1). Fecal E. coli concentrations were affected by treatment (P < 0.01), showing the highest values (log10 CFU/g) in fecal contents from mimosa-fed steers compared to controls (5.9 versus 5.6 ± 0.1 SEM, respectively). Total coliforms (log CFU/g) showed the highest values (P < 0.01) in feces from chestnut- and mimosa-fed steers (6.0 and 6.1 ± 0.1, respectively) in comparison with controls (5.7 ± 0.1). Fecal Campylobacter concentrations (log10 CFU/g) were affected by treatment (P < 0.05), day (P < 0.001), and their interaction (P < 0.01) with the controls having lower concentrations than chestnut- and mimosa-fed steers (0.4, 1.0, and 0.8 ± 0.3, respectively). It was concluded that under our research conditions, tannins were not effective in decreasing measured bacterial populations on beef cattle hides. Additionally, chestnut tannin reduced E. coli and total coliforms within the rumen, but the antimicrobial effect was not maintained in the lower gastrointestinal tract. Further research is necessary to elucidate the possible antimicrobial effects of tannins at site-specific locations of the gastrointestinal tract in beef cattle fed high-grain and high-forage diets.