Polyphenolic constituent structures of Zanthoxylum piperitum fruit and the antibacterial effects of its polymeric procyanidin on methicillin-resistant Staphylococcus aureus

Zanthoxylum piperitum (Rutaceae) is used as a spice and a natural medicine in Japan. Our study found that ZP-CT-A, a polymeric proanthocyanidin purified from the fruit of this species, noticeably decreased the minimum inhibitory concentrations of β-lactam antibiotics for methicillin-resistant Staphylococcus aureus (MRSA). The structure of ZP-CT-A was characterized on the basis of ¹³C NMR and size exclusion chromatographic data and the results of thiolytic degradation. A mechanistic study of the effects of ZP-CT-A indicated that it suppressed the activity of β-lactamase and largely decreased the stability of the bacterial cell membrane of MRSA, as shown by a reduction in the tolerance of MRSA to low osmotic pressure and high ionic strength solutions.