Diterpenoids of Caryopteris trichosphaera W. W. Sm. inhibiting MRSA and VRE in vitro and in vivo

Ethnopharmacological relevance

Caryopteris trichosphaera W. W. Sm., a traditional ethnic medicine, was recorded in the Compendium of Materia Medica for treating wound infection by pathogenic infection. However, its antibacterial potential and bioactive compositions against drug-resistant bacteria need to be validated.

Aim of the study

To investigate the chemical constituents of C. trichosphaera and explore its anti-MRSA component in vitro and in vivo, together with the antibacterial mechanism.

Materials and methods

Bioactive constituents investigation was carried out by phytochemical method and antibacterial screening. The antibacterial mechanism was predicted by network pharmacology, which was further validated by time-kill analysis, membrane function tests, multigenerational resistance induction assay and biofilm test, and metabolomics analysis in vitro. In addition, MRSA-induced epidermal infection in mice was selected to evaluate its pharmacological effect in vivo.

Results

Six antibacterial diterpenoids against MRSA and VRE with MIC values 4–32 μg/mL from C. trichosphaera were reported for the first time, in which the major compound cativic acid (1) disrupted MRSA cell membranes by modulating permeability, depolarization, and fluidity while increasing reactive oxygen species (ROS) and malondialdehyde (MDA) levels. It also displayed remarkable anti-biofilm activity without inducing bacterial resistance or cytotoxicity. Moreover, cativic acid affected MRSA biosynthesis of cofactors, amino acid biosynthesis, nucleotide metabolism by metabolomics analysis. Furthermore, cativic acid accelerated wound healing in MRSA-infected mouse skin wounds, even better than vancomycin.

Conclusions

The results supported the traditional use of C. trichosphaera, and presented unreported anti-MRSA agent, cativic acid, as a plant-derived bactericide in vitro and in vivo for the first time.