The aim of this study was to quantify and evaluate the antibacterial activity of tannins extracted from leaves of Psidium guineense, obtained using two different isolation methods, against Staphylococcus aureus and Pseudomonas aeruginosa. The first extraction method was used to isolate condensed tannins (Method A) and the second to isolate mixtures rich in esters of gallic acid and glucose (Method B). Both extraction methods yielded high concentrations of tannins, with 312 and 257 mg/g of dry material obtained using Methods A and B, respectively. These compounds formed halos of growth inhibition in S. aureus and P. aeruginosa cultures. Tannins isolated by method B gave rise to larger inhibition halos than those isolated by method A. Analysis of the antibacterial activity of tannins isolated by method B revealed a minimum inhibitory and bactericidal concentration of 256 μg/ml for S. aureus and 512 μg/ml for P. aeruginosa. These results demonstrate that P. guineense is a promising source of pharmacologically active tannin molecules, and further studies are therefore necessary to determine the toxicity of the plant and ensure its safe use for animal and human health.

In vitro tests conducted with extracts rich in tannins have identified several biological activities of this class of substance. Thus, this paper intends to evaluate the antibacterial activity of tannin-rich fraction obtained from leaf extracts of