Plants of the Cerrado with antimicrobial effects against Staphylococcus spp. and Escherichia coli from cattle

BACKGROUND Both diarrhea in calves and mastitis in cows limit cattle production. The bacteria involved in these diseases have shown multi-resistance to antimicrobials, however plant metabolites therefore can provide an alternative method of control. This study selected and characterized Cerrado plant extracts showing inhibitory effects against Escherichia coli and Staphylococcus spp. from cattle. Thirteen leaf extracts were initially screened and diameters of inhibition zones produced against the pathogens were recorded using an agar disk diffusion method. Total condensed tannin contents were determined and antibacterial activities were analyzed after tannin removal from the five selected extracts. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were evaluated by macro-dilution antimicrobial susceptibility tests, and the extracts were characterized by high performance liquid chromatography. RESULTS Inter- and intra-specific bacterial variations in the susceptibility to the extracts were detected. The aqueous extract (AE) from Caryocar brasiliense Cambess. leaves produced larger inhibition zones against E. coli strains than did other selected extracts. However, the AE from Schinopsis brasiliensis was the most effective against Staphylococcus spp. strains (P < 0.001). The MIC of ethanolic extracts (EE) from C. brasiliense (0.27 mg/mL) and S. brasiliensis (0.17 mg/mL) were lower than those of other extracts. The MIC and MBC of the Annona crassiflora EE were 6.24 mg/mL for all bacteria. Flavonoids were the main metabolites detected in the A. crassiflora EE as well as in the AE and EE from C. brasiliense, while tannins were the main metabolites in the S. brasiliensis leaf extracts. CONCLUSION The AE from C. brasiliense was more effective against Gram-negative bacteria, while the AE from S. brasiliensis was more effective against Gram-positive bacteria. A. crassiflora EE and S. brasiliensis extracts are potent bactericide. After removal of the tannins, no antimicrobial effects were observed, indicating that these metabolites are the main active antibacterial components.