Submitted to: Scientific Research and Essays
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/19/2007
Publication Date: 2/1/2008
Citation: Min, B., Pinchak, W., Merkel, R., Walker, S., Tomita, G., Anderson, R.C. 2008. Comparative antimicrobial activity of tannin extracts from perennial plants on mastitis pathogens. Scientific Research and Essays. 3(2):66-73. Interpretive Summary: Certain strains of Staphylococcus aureus and Escherichia coli can cause economically important disease in dairy cattle and can be found as contaminants in unpasteurized milk. This study was conducted to test the antimicrobial effectiveness of a specific class of naturally occurring chemicals called tannins, found in certain plants, against these pathogenic bacteria. We found that tannin chemicals extracted from Shinnery oak, Post oak, Locust, Blackjack oak, Skunk bush, Sericea lespedeza, commercial Quebracho, Sumac, and Plum plants inhibited the growth of Staphylococcus aureus, with effectiveness being best with tannins from Shinnery oak and Post oak. When chemical components of the tannin extracts were separated based on their chemical properties and tested individually against Staphylococcus aureus and Escherichia coli, we found that the antimicrobial activity was greatest for compounds classified as catechins and less for compounds classified as ellagetannins, tannic acid, epi-catechin, and gallotannins. These findings indicate that source, concentration, and chemical properties are important factors that influence antimicrobial activity of tannin extracts. Our results also revealed that some of the plant tannin extracts were highly effective against these pathogens, inhibiting their growth as much or better than that of the common antibiotic Penicillin, which suggests that they may be useful alternatives to conventional antimicrobial feed additives. Ultimately, these results may provide farmers with additional tools to control infections in their cattle so they can continue to produce wholesome, high quality food products for the American consumer.
Technical Abstract: Three strains of pathogenic bacteria were treated with condensed tannins (CT) purified from eight different woody plant species to investigate their inhibition effect on the growth of these bacteria in vitro. Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus were tested against low (0, 2, 4 and 8 mg CT/ml) and high dose levels (0, 50, and 100 mg CT /ml) of CT extracted from different plant species. When exposed to purified tannin extracts at 4 mg extract/ml dosage, growth inhibition of S. aureus was dose dependent and observed in the following order: Shinnery oak greater than Post oak greater than Locust greater than Blackjack oak greater than or equal to Skunk bush greater than Sericea lespedeza greater than commercial Quebracho greater than or equal to Sumac greater than Plum. The extracts from Shinnery and Post oaks were particularly inhibitory against S. aureus, having growth inhibition zones exceeding 23 mm at 8 mg tannin extract/ml. Staphylococcus aureus and E. coli exhibited dose dependent susceptibility (P less than 0.01) when exposed to greater than or equal to 4 mg/ml of the following tannin monomers with inhibitory activity observed in the following order: catechin greater than ellagetannin greater than or equal to tannic acid greater than or equal to epi-catechin greater than or equal to gallotannin. In the presence of high dose levels at 0, 50, and 100 mg tannin extract/ml, inhibition zones of growth were varied among plant species. The findings indicated that source and concentration are important factors that influence antimicrobial activity of tannins. Because some of the plant tannin extracts are highly inhibitory to selected pathogens, they may provide alternatives to conventional antimicrobial feed additives.