European Journal of Medicinal Plants

Aims: Research on natural antimicrobials has increased due to the emergence of microbial strains resistant to conventional antibiotics. We investigated and report here the in vitro antibacterial properties of crude extracts from Brazilian savanna plants (Achyrocline satureioides (Lam.) DC (“macela”), Stryphnodendron adstringens (Mart.) Coville (”barbatimão”), Miconia rubiginosa (Bonpl.) DC (“quaresma branca”), Davilla elliptica A. St.-Hil. (“lixinha”), Siparuna guianensis (“negramina”) and Solanum lycocarpum A. St.-Hil. (“lobeira”).

Place and Duration of Study: Department of Microbiology and Immunology, Biosciences Institute, São Paulo State University from January 2010 to December 2011.

Methodology: Antibacterial activities were investigated using two methods: the disk diffusion method against American Type Culture Collection bacterial strains (Staphylococcus aureus – ATCC 25923, Escherichia coli – ATCC 22652, and Pseudomonas aeruginosa – ATCC 27853) and the susceptibility assays by agar dilution method (Mueller Hinton Agar (MHA) aiming the minimal inhibitory concentrations (MIC) and MIC_90% (mg.mL^-1), against S. aureus, E. coli and P. aeruginosa strains isolated from human clinical specimens. Qualitative phytochemical analysis of crude extracts was also performed.

Results: By agar dilution test, the D. elliptica leaf extract was efficient against all strains (MIC_90% values of 0.7, 2.6, and 2.1 mg.mL^-1 against S. aureus, E. coli, and P. aeruginosa, respectively), while the S. guianensis leaf extract showed the lowest activity (12.2, >32.0, and 26.0 mg.mL^-1 against S. aureus, E. coli, and P. aeruginosa, respectively). We detected flavonoids and phenolic compounds in all studied extracts.

Conclusion: All studied extracts showed antibacterial activity by the agar dilution method, although M. rubiginosa and S. guianensis leaves extracts did not show inhibitory action against E. coli and P. aeruginosa strains. There was a greater sensitivity of S. aureus and the D.elliptica leaf extract showed the highest efficiency over most of the strains tested. Additionally, the results show that it is possible to obtain conflicting results using the disk diffusion method and the dilution method.