326 Activities and screening of Yemeni medicinal plant Table 2. Results of the antimicrobial activity of the investigated plants in agar diffusion method Plant species Extracts Extract yield (%) Microbial strains tested Multiresistant strains tested S. a. B. c. M. f. E. c. P. e. C. m. S. e. 847 S. h. 535 S. a. North German epidemic strain Acalypha fruticosa Methanolic 8.8 14 14 21 – – – 12 – 10 Hot aqueous 5.2 – – – – – – – – – Actiniopteris semiflabellata Methanolic 11.9 11 9 14 – – – – – – Hot aqueous 8.1 – – – – – – – – 20 Alkanna orientalis Methanolic 17.5 10 10 14 – – – 18 20 16 Hot aqueous 6.9 – – – – – – 16 – 8 Carthamus tinctorius Methanolic 10.2 12 9 12 – – – 12 – – Hot aqueous 6.4 – – – – – – – – 16 Centaurea pseudosinaica Methanolic 13.1 13 13 14 – – – 14 12 – Hot aqueous 7.9 – – – – – – – – 10 Cleome schweinfurthii Methanolic 8.8 10 10 14 – – – – 8 – Hot aqueous 4.7 – – – – – – – – 14 Dodonaea viscosa Methanolic 10.0 15 11 21 – – – 12 10 12 Hot aqueous 7.3 14 8 16 – – – 12 – – Forsskalea tinacissima Methanolic 5.3 9 – 10 – – – – – – Hot aqueous 4.2 – – – – – – – – 8 Iris albicans Methanolic 10.9 10 10 14 – – – 12 10 – Hot aqueous 9.4 – – – – – – – – 12 Jatropha variegata Methanolic 9.8 16 10 16 – – – 12 12 – Hot aqueous 6.8 – – – – – – – – 12 Lavandula pubescens Methanolic 8.0 14 11 12 – – – 12 12 18 Hot aqueous 4.9 – – – – – – 18 16 22 Lippia citriodora Methanolic 8.4 17 13 17 – – – 20 20 – Hot aqueous 5.7 – – – – – – – – Mentha longifolia Methanolic 10.0 11 9 11 – – – 14 10 14 Hot aqueous 6.8 – – – – – – 22 18 20 Plectranthus hadiensis (Leaves) Methanolic 9.8 12 11 20 – – – 12 10 12 Hot aqueous 7.1 12 9 9 – – – 14 10 14 Plectranthus hadiensis (Roots) Methanolic 7.9 16 14 20 – – – 24 16 22 Hot aqueous 5.0 – – – – – – 18 8 16 Tragia pungens Methanolic 9.9 14 11 14 – – – 18 8 12 Hot aqueous 5.9 8 – – – – – 14 – 12 Verbascum bottae Methanolic 19.7 13 9 14 – – – 10 – 10 Hot aqueous 14.8 – – – – – – – – – Ampicillin 10 mg/disc 25 26 30 N.T. N.T. N.T. – – – Gentamicin 10 mg/disc N.T. N.T. N.T. 15 17 N.T. N.T. N.T. N.T. Amphotericin 10 mg/disc N.T. N.T. N.T. N.T. N.T. 10 N.T. N.T. N.T. S. a., Staphylococcus aureus ATCC 6538; B. c., Bacillus subtilis ATCC 6059; M. f., Micrococcus flavus SBUG 16; E. c., Escherichia coli ATCC 11229; P. e., Pseudomonas aeruginosa ATCC 27853; C. m., Candida maltosa SBUG; S. e. 847, multiresistant Staphylococcus epidermidis; S. h. 535, multiresistant Staphylococcus haemolyticus; S. a. North German species, multiresistant Staphylococcus aureus; –, no activity; N.T., not tested; Inhibition zones including the diameter of the paper disc (6 mm). V. bottae showed a high effective free radical scavenging in the DPPH assay. These extracts exhibited a remark- able antioxidant effect at low concentrations. So the methanolic extracts of A. fruticosa and T. pungens exhibited at 10 mg ml 1 an extraordinary antioxidant effect (43% and 54% successively) whereas the ascorbic acid showed at this concentration an effect of 45% (Table 3). A. semiflabellata, D. viscosa and P. hadiensis started to exhibit a high effective free radical scavenging at 50 mg ml 1 (55, 50 and 54%, respectively). The water extracts of all investigated plants were only weak active. The free radical scavenging effect ranged between 10 and