title: Isopimaric acid from Pinus nigra shows activity against multidrug-resistant and EMRSA strains of Staphylococcus aureus.
abstract: The diterpene isopimaric acid was extracted from the immature cones of Pinus nigra (Arnold) using bioassay-guided fractionation of a crude hexane extract. Isopimaric acid was assayed against multidrug-resistant (MDR) and methicillin-resistant Staphylococcus aureus (MRSA). The minimum inhibitory concentrations (MIC) were 32-64 microg/mL and compared with a commercially obtained resin acid, abietic acid, with MICs of 64 microg/mL. Resin acids are known to have antibacterial activity and are valued in traditional medicine for their antiseptic properties. These results show that isopimaric acid is active against MDR and MRSA strains of S. aureus which are becoming increasingly resistant to antibiotics. Both compounds were evaluated for modulation activity in combination with antibiotics, but did not potentiate the activity of the antibiotics tested. However, the compounds were also assayed in combination with the efflux pump inhibitor reserpine, to see if inhibition of the TetK or NorA efflux pump increased their activity. Interestingly, rather than a potentiation of activity by a reduction in MIC, a two to four-fold increase in MIC was seen. It may be that isopimaric acid and abietic acid are not substrates for these efflux pumps, but it is also possible that an antagonistic interaction with reserpine may render the antibiotics inactive. 1H-NMR of abietic acid and reserpine taken individually and in combination, revealed a shift in resonance of some peaks for both compounds when mixed together compared with the spectra of the compounds on their own. It is proposed that this may be due to complex formation between abietic acid and reserpine and that this complex formation is responsible for a reduction in activity and elevation of MIC.
authors.affiliation: Centre for Pharmacognosy and Phytotherapy, The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1AX, UK.
authors.forename: Eileen
authors.initials: E
authors.lastname: Smith
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Williamson
authors.forename: Mire
authors.initials: M
authors.lastname: Zloh
authors.forename: Simon
authors.initials: S
authors.lastname: Gibbons
mesh_terms: D045784:Abietanes / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D002264:Carboxylic Acids / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D010616:Phenanthrenes / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D008517:Phytotherapy; D028223:Pinus; D010936:Plant Extracts / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects*; D013237:Stereoisomerism
chemical_list: D045784:Abietanes; D000900:Anti-Bacterial Agents; D002264:Carboxylic Acids; D010616:Phenanthrenes; D010936:Plant Extracts; C115138:isopimaric acid; C023710:abietic acid