Development of novel agents to treat infections caused by multidrug-resistant bacteria
is an urgent priority. Medicinal plants are a recognised source of diverse bioactive
compounds with
capacities to tackle such organisms [1]. The root of Salvia miltiorrhiza Bunge (red sage or Danshen, Lamiaceae) has been used traditionally to treat coronary
heart diseases, although S.miltiorrhiza extracts have also been shown to possess antimicrobial activities against a range
of pathogenic organisms [2], [3].
The aim of this study was to investigate metabolites from S.miltiorrhiza previously uncharacterised in terms of antimicrobial activities and potential to
negate efflux-mediated
resistance in Staphylococcus aureus. These metabolites were tanshinone I, tanshinone
IIA, cryptotanshinone, dihydrotanshinone, salvianolic acid A, Miltirone, protocatechuicaldhyde,
rosmarinic
acid, caffeic acid and danshensu. Minimum inhibitory concentrations (MICs) and
minimum bactericidal concentration (MBC) assays were determined against S. aureus ATCC25 923,
SA-1199B+NorA (expressing the NorA efflux pump) and XU212+TetK (expressing the
TetK efflux pump). Miltirone and dihydrotanshinone had the lowest MIC values; 0.5 – 1 µg/mL.
The MBC values of
Miltirone for S. aureus ATCC25 923 was 2 µg/mL, for SA-1199B+NorA and XU212+TetK was 4 µg/mL. However, the
MBC value for dihydrotanshinone was > 128 µg/mL for all S. aureus
strains, indicating bacteriostatic activities. At sub-inhibitory concentrations,
both metabolites potentiated the activities of tetracycline and norfloxacin, yielding
a 2- or 4-fold reduction
in MICs against S.aureus XU212+TetK and SA-1199B+NorA, respectively. The MIC of the other metabolites ranged
between 512 – 64 µg/mL.
Overall, evaluation of these compounds indicates that they could be drug leads in
managing staphylococcal infections.
