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.
Keywords: Ampicillin; checkerboard assay; flow cytometry; myticaganal C; synergistic effect.
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