Antimicrobial Activity of Salvia corrugata exudate against Human Pathogenic Bacteria.

The surface exudate of fresh aerial parts of Salvia corrugata Vahl. showed a significant in vitro activity against several clinically important Gram-positive species, while Gram-negative organisms were not affected. The active principles of this extract were identified as the isomeric triterpenes ursolic acid and oleanolic acid and the highly oxidized diterpene quinones fruticuline A (1) and demethylfruticuline A (2) by spectroscopic NMR analysis. Until now, these two compounds have been isolated only from S. fruticulosa Benth. [1, 2] and S. arizonica Gray [3]. The interpretation of proton and carbon signals of these diterpenoids were largely consistent with those reported in literature, however, on the basis of DEPT, HSQC and HMBC experiments, some assignments were revised. For these compounds the extractive yield was reported in the cited works only for the first species: 0.0026 % for 1 and 0.01 % for 2 (dry weight); moreover, their biological activity was not yet demonstrated. As for the above cited species, the most abundant diterpenoid product isolated from Salvia corrugata is demethylfruticuline A. The obtained extractive yields of 1 and 2 from fresh aerial parts were 0.029 % and 0.11 %, respectively. This result is consistent with the quantitative HPLC determination of 1 and 2, which showed that the exudate contained 6.5 ± 0.3 % of 1 and 33.6 ± 0.8% of 2 corresponding to theoretical extractive yields of 0.060 % and 0.30 % from the fresh aerial parts, respectively. As the antimicrobial activity of ursolic and oleanolic acid has been previously described, we focused this study only on the diterpene quinones. The antimicrobial in vitro activity of compounds 1 and 2 was assessed against two Vancomycin-susceptible (VAN-S) Enterococcus faecalis, four Vancomycin-resistant (VAN-R) E. faecalis, one VAN-S E. faecium and five VAN-R E. faecium; five Oxacillin-susceptible Staphylococcus aureus (OXA-S), nine Oxacillin-resistant (OXA-R) S. aureus, four multidrug-resistant S. aureus, four OXA-S S. epidermidis and five OXA-R S. epidermidis. Minimum Inhibitory Concentrations (MICs) were determined according to CLSI guidelines [4]. The distribution of MICs for all pathogens ranged from 32 to 64 mg/L, irrespectively of their resistance patterns to other antibiotics. Compound 1 was shown to be highly bactericidal (>3 log CFU killing within 24 hours) for Staphylococcus species while its activity was bacteriostatic for the Enterococci. Compound 2 manifested a bacteriostatic activity on all tested strains. If well tolerated in vivo, the antimicrobial compounds described here may represent useful new medicaments to be employed in serious infections sustained by hard-to-eradicate Gram-positive pathogens. Riferimenti [1] L. Rodriguez-Hahn, B. Esquivel, C. Sánchez, J. Cárdenas, L. Estebanes, M. Soriano-García, R. Toscano, T.P. Ramamoorthy Tetrahedron letters 1986, 27, 5459-5462, [2] L. Rodriguez-Hahn, B. Esquivel, C. Sánchez, L. Estebanes, J. Cárdenas, M. Soriano-García, R. Toscano, T.P. Ramamoorthy Phytochemistry 1989, 28, 567-570; [3] K.M. Valant-Vetschera, J.N. Roitman, E. Wollenweber Biochem. Suyst. Ecol. 2003, 31, 1279-1289. [4] Clinical and Laboratory Standards Institute, Vol. 27, 2007.