Antibacterial properties of phenolic triterpenoids against Staphylococcus epidermidis

Two phenolic triterpenoids, pristimerol (30 μg/mL) and 8- EPI-6-deoxoblepharodol (20 μg/mL), obtained by catalytic reduction of pristimerin, exhibited bacteriostatic action against Staphylococcus epidermidis. This activity was not dependent on the inoculum size and the growth phase although it showed a stronger effect when cells were growing actively. Addition of phenolic triterpenoids to S. epidermidis cultures in the log-phase of growth led to an inhibitory effect on incorporation and uptake of radiolabeled precursors thymidine, uridine, leucine, and N-acetyl-glucosamine after 30 min of treatment. Furthermore, a clear release of UV-absorbing material and leakage of intracellular potassium were also detected. These findings, coupled with the high lipophilicity of these molecules, shown by high ClogP values, suggest that 8-EPI and pristimerol are able to interact within the lipid bilayer and as a consequence cause functional alterations on the cytoplasmic membrane of S. epidermidis cells.