Abietanes from Plectranthus grandidentatus and P. hereroensis against methicillin- and vancomycin-resistant bacteria

The antimicrobial activity of 10 natural abietanes isolated from Plectranthus grandidentatus and P. hereroensis acetonic extract was evaluated against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecalis (VRE). The results revealed that the most active diterpenes were coleon U (1), 7α-acetoxy-6β-hydroxyroyleanone (2) and horminone (3). Minimum inhibitory concentration (MIC) values ranging 0.98–15.63 μg/ml were obtained for MRSA clinical strains, and MIC values of 15.63 and 31.25 μg/ml were obtained for VRE clinical strains. Some structure–activity relationships are emphasized.