Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2006
Publication Date: 3/20/2007
Citation: Min, B.R., Pinchak, W.E., Anderson, R.C., Callaway, T.R. 2007. Effect of tannins on the in vitro growth of Escherichia coli O157:H7 and in vivo growth of generic Escherichia coli excreted from steers. Journal of Food Protection. 70:543-550. Interpretive Summary: Escherichia coli O157:H7 is an important foodborne pathogen that can reside in the gastrointestinal tract of cattle. Because this pathogen can contaminate ground beef, strategies are sought to reduce carriage of this pathogen in cattle before they arrive for processing. A laboratory experiment was conducted to test if commercially available chestnut and mimosa tannins, compounds normally found in some plants, would inhibit the growth Escherichia coli O157:H7. We found that the average growth rate of E. coli O157:H7 was significantly reduced when experimental cultures were grown with as little as 400 ug of either tannin extract per ml of culture fluid when compared with the control cultures grown without the tannin extracts. Another experiment was conducted to test if the inhibitory effect of chestnut tannin against E. coli could be achieved in animals. When chestnut tannin extract (15 g per day) were infused intraruminally to steers fed a Bermuda grass hay diet, fecal E. coli shedding was lower on days 3, 12, and 15 of treatment when compared with animals that were fed a similar diet without tannin supplementation. These results suggest that dietary levels and sources of tannins can reduce the shedding of E. coli from the gastrointestinal tract of cattle. Ultimately, these results may lead to the development of low cost treatment strategies to help cattle producers continue to grow and provide safe and wholesome meat products for the American consumer.
Technical Abstract: The effect of commercially available chestnut and mimosa tannins in vitro (experiment 1) or in vivo (experiment 2) on the growth or recovery of Escherichia coli O157:H7 or generic fecal E. coli was evaluated. In experiment 1, the mean growth rate of E. coli O157:H7, determined via the measurement of optical density at 600 nm during anaerobic culture in tryptic soy broth at 37 deg C, was reduced (P < 0.05) with as little as 400 ug of either tannin extract per ml of culture fluid. The addition of 200, 400, 600, 800, and 1,200 ug of tannins per ml significantly (P < 0.01) reduced the specific bacterial growth rate when compared with the nontannin control. The specific growth rate decreased with increasing dose levels up to 800 ug of tannins per ml. Bacterial growth inhibition effects in chestnut tannins were less pronounced than in mimosa tannins. Chestnut tannin extract addition ranged from 0 to 1,200 ug/ml, and a linear effect (P < 0.05) was observed in cultures incubated for 6 h against the recovery of viable cells, determined via the plating of each strain onto MacConkey agar, of E. coli O157:H7 strains 933 and 86-24, but not against strain 6058. Similar tests with mimosa tannin extract showed a linear effect (P < 0.05) against the recovery of E. coli O157:H7 strain 933 only. The bactericidal effect observed in cultures incubated for 24 h with the tannin preparations was similar, although it was less than that observed from cultures incubated for 6 h. When chestnut tannins (15 g of tannins per day) were infused intraruminally to steers fed a Bermuda grass hay diet in experiment 2, fecal E. coli shedding was lower on days 3 (P < 0.03), 12 (P = 0.08), and 15 (P < 0.001) when compared with animals that were fed a similar diet without tannin supplementation. It was concluded that dietary levels and sources of tannins potentially reduce the shedding of E. coli from the gastrointestinal tract.