Evaluation of the antimicrobial potency of tannins and related compounds using the microdilution broth method

The antimicrobial activity of a total of 27 tannins and related compounds was evaluated against 8 microorganisms, including 2 Gram-positive (Bacillus subtilis, Staphylococcus aureus), 4 Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis), and 2 yeasts (Candida albicans, Cryptococcus neoformans). The compounds tested were generally found to possess only weak to moderate antibacterial, but fairly high anticryptococcal activities. Attention is given to structure-activity relationships with emphasis on simple galloyl esters, hydrolyzable tannins and proanthocyanidins among this class of secondary products.