Comparative antimicrobial activity of tannin extracts from perennial plants on mastitis pathogens

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 manner and observed in the following order: Shinnery oak > Post oak > Locust > Blackjack oak ≥ Skunk bush > Sericea lespedeza > commercial Quebracho ≥ Sumac > 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.  S. aureus andE. coli exhibited dose dependent and susceptibility (P  ellagetannin ≥ tannic acid ≥ epi-catechin ≥ 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 and supplements to conventional antimicrobial feed additives.   Key words: Pathogenic bacteria, tannins, tree leaves, zone of inhibition.