Stephania suberosa Forman extract synergistically inhibits ampicillin- and vancomycin-resistant Enterococcus faecium.

Increasing antibiotic resistance in enterococci is among the most serious public health problems worldwide. The new naturally occurring antibacterial agents were explored. This study, therefore, investigated the antibacterial potential of extract (SSE) and its synergism with ampicillin (AMP) or vancomycin (VAN) against AMP- and VAN-resistant . Disc diffusion assay revealed that SSE inhibited DMST 12829, 12852, 12970, and a reference strain of ATCC 29,212 in a dose-dependent manner. The minimum inhibitory concentration (MIC) of SSE against all isolates was 0.5 mg/mL. DMST 12,829 and 12,852 were highly resistant to AMP, as indicated by high MIC values, and DMST 12,829 and 12,970 were resistant to VAN. spp. were killed by SSE at the minimum bactericidal concentrations (MBCs) ranging from 0.5 to 4 mg/mL. Checkerboard determination showed that SSE plus AMP and SSE plus VAN combinations exhibited synergistic interaction against isolates. The killing curve assay of isolates confirmed the antibacterial and synergistic activities of combined agents by dramatically reducing the viable counts compared to a single agent. Scanning electron microscope elucidated the cell damage and abnormal cell division. Enterococcal proteases were also inhibited by SSE. These findings support that SSE could reverse the activity of AMP and VAN. Moreover, it can synergistically inhibit AMP- and VAN-resistant . Our combined agents could be attractive candidates for developing new combinatorial agents to resurrect the efficacy of antibiotics for treating AMP- and VAN-resistant infections.