Abstract

Infections caused by multidrug-resistant bacteria are a problem of public health, turning the search for natural products an alternative to antibiotics of great importance. The aim of this study was to investigate the in vitro antimicrobial activities of Hymenaea courbaril and Stryphnodendron adstringens against bacterial clinical isolates. The crude extracts of both vegetal species in study showed bacteriostatic activity against almost all bacteria evaluated, with minimum inhibitory concentration (MIC) ranging from 125 to 1250 µg/ml. The bacteriostatic activity was observed in all the fractions of H. courbaril and S. adstringens against at least one bacterial strain, except in the fraction dichloromethane of S. adstringens. In regard to bactericidal activity, H. courbaril was active only against E. faecalis, and S. adstringens showed activity against all bacterial strains, except to Enterococcus faecalis. The combination of extracts showed potent synergistic antimicrobial activity, with MIC values of 31.25 µg/ml against Acinetobacter baumannii, Escherichia coli and Staphylococcus aureus. S. adstringens were considered less cytotoxic compared to H. courbaril and the half-maximum cytotoxic concentration (CC₅₀) resulting from the combination of the two plants was 0.0082 ± 3.19 mg/ml. The results showed for the first time the synergic antibacterial activities of H. courbaril and S. adstringens against resistant bacteria, suggesting their potential use to development of new drugs.

Key words: Hymenaea courbaril, Stryphnodendron adstringens, antimicrobial activity, synergism, multidrug-resistant bacteria.