Abietane diterpenes from the cones of Abies numidica de Lannoy ex Carrière (Pinaceae) and in vitro evaluation of their antimicrobial properties

Eight known abietane diterpenes (1–8) were isolated for the first time from Abies numidica cones (Pinaceae). The structures of all compounds were established by means of 1D and 2D NMR, and UV spectral analyses. The hydromethanolic extract of A. numidica cones was tested for its antimicrobial activity against 17 gram-positive and gram-negative bacteria and against five yeasts by the use of liquid and solid medium and bioautography methods. The best antimicrobial activity was found against gram-positive bacteria (MIC ≤ 0.3 mg/mL) Bacillus subtilis, Enterococcus faecalis ATCC 1034, Staphylococcus aureus 8325.4, S. aureus CIP 53.154, Micrococcus luteus and Listeria innocua and against Candida yeasts. The determination of MIC’s of isolated products showed a high activity of compounds 4 and 6 against S. aureus, L. innocua (MIC = 62.5 μg/mL) and E. faecalis (MIC = 125 μg/mL).