Screening of several plant extracts for antimicrobial potential

Dissertação de mest., Engenharia Biológica, Faculdade de Engenharia de Recursos Naturais, Universidade do Algarve, 2008The aim of this study was to evaluate the antimicrobial activity of plant extracts from Lavandula viridis, Drosera rotundifolia, Drosera intermedia and Pinguicula lusitanica, obtained with different extraction techniques, against various yeasts and bacteria species, including both reference and clinically isolated strains. The antimicrobial activity of the extracts was evaluated by the disc diffusion method and the determination of minimum inhibitory concentration (MIC) in liquid media. All tested microorganims were affected by L. viridis essential oil, which proved to be the most active extract of this plant, presenting higher antimycotic activity than antibacterial one. Although Gram-negative bacteria were less affected (when compared with Gram-positive bacteria), the hexane extract from D. intermedia presented higher antibacterial activity than all other extracts tested (except for P. aeruginosa ATCC 27853, which was tolerant); it also showed the overall highest antimycotic activity. D. rotundifolia extract presented antibacterial activity against all species except one (E. faecalis ATCC 29212) and affected Gram-negative bacteria in a similar way as nonhexane extracts of D. intermedia did. These plant species also presented antimycotic activity against all yeasts tested. From the plant species tested, P. lusitanica proved to be the least antimicrobial active one, tolerated by almost all species (except Grampositive S. aureus ATCC 25923 and S. epidermidis ATCC 12228). Furthermore, the clinically isolated yeasts, which are resistant to flucozanole, were found to be sensitive to L. viridis essential oil, and D. intermedia and D. rotundifolia extracts. The less affected microroganisms were Gram-positive bacteria E. faecalis ATCC 29212, Gram-negative bacteria P. aeruginosa ATCC 27853 and yeast C. famata YP0011. The results obtained, which are consistent with the reported ethnobotanical use of the tested plants, represent promising possibilities as new natural bioactive drugs. However, further tests are necessary to access which substances/pathways are responsible for the antimicrobial activity detected in these plant extracts