Synergistic effect of ampicillin and dihydrobenzofuran neolignans (myticaganal C) identified from the seeds of Myristica fragrans Houtt. against Escherichia coli

The present study was designed to enhance the antibacterial activity of ampicillin against Escherichia coli by combining it with myticaganal C. Antibacterial activity of ampicillin combined with myticaganal C against E. coli was assessed by agar well diffusion. Minimum inhibitory concentrations (MICs) and synergy by checkerboard assay of ampicillin and myticaganal C were assessed by resazurin-based 96-well microdilution. Bacterial responses were assessed by flow cytometry. Ampicillin in combination with myticaganal C showed better zone of inhibition (31.67 ± 0.58 mm) than myticaganal C or ampicillin alone. MIC of ampicillin was found to be 12.5 μg/mL, but myticaganal C was ineffective against E. coli. Myticaganal C (8000 μg/mL) with ampicillin (0.0975 μg/mL) exhibited strong synergy, so the need for ampicillin was reduced 128-fold. Combination inhibited E. coli by acting on cell membrane and by granularity disruptions. These findings indicate that myticaganal C enhances the potential of ampicillin against E. coli, thus providing an effective alternative to deal with the problem of bacterial resistance.