Antibacterial properties of zeylasterone, a triterpenoid isolated from Maytenus blepharodes, against Staphylococcus aureus

SummaryThe anti-staphylococcal properties of zeylasterone and demethylzeylasterone, two 6-oxophenolic triterpenoids isolated from Maytenus blepharodes, were investigated. Zeylasterone was more active than demethylzeylasterone on Staphylococcus aureus cells, showing bactericidal activity at 30 μg/ml (6×MIC) in less than three hours and bacteriostatic at lower concentrations. At the same cell density, a more drastic reduction in CFU count was obtained when the triterpenoid was incorporated into cultures growing actively. Zeylasterone at 3×MIC added on S. aureus cultures showed an early inhibitory effect on incorporation of radiolabeled thymidine, uridina and N-acetyl-glucosamine, and later on leucine. It also caused cell membrane disruption in S. aureus, as shown by the inhibition of radiolabeled precursor uptake, rapid potassium leakage, inhibition of NADH oxidation, and formation of mesosome-like structures around the septa. The structural features of the molecule, the blockage of solute transport through the membrane and changes in its permeability, suggest that zeylasterone acts mainly on cytoplasmic membrane.