Objective To investigate the inhibitory effect of tannic acid and different ratios of cefoperazone sodium to sulbactam sodium on carbapenem-resistant Acinetobacter baumannii (CRAB).

Methods The minimum inhibitory concentrations (MICs) of tannic acid, the ratio of 1∶ 1 for cefoperazone sodium/sulbactam sodium and the ratio of 2∶ 1 for cefoperazone sodium/sulbactam sodium against six strains of CRAB were determined by micro-broth dilution method; the MIC of tannic acid combined with cefoperazone sodium-to-sulbactam sodium ratio against CRAB was determined by checkerboard dilution method, and the partial inhibitory concentration index (FICI) was calculated.

Results The MIC of tannic acid for the six strains of CRAB ranged from 128 μg/mL to 256 μg/mL; the MIC of cefoperazone sodium-to-sulbactam sodium ratio(1∶ 1) for six strains of CRAB ranged from 32 μg/mL to 128 μg/mL; the MIC of cefoperazone sodium-to-sulbactam sodium ratio(2∶ 1) for six strains of CRAB ranged from 64 μg/mL to 256 μg/mL; the FICI of tannic acid combined with cefoperazone sodium-to-sulbactam sodium(1∶ 1) was ranged from 0.375 to 0.750, showing synergistic and additive effects.

Conclusion Cefoperazone sodium-to-sulbactam sodium ratio(1∶ 1) is more effective in bacterial inhibition for CRAB than cefoperazone sodium-to-sulbactam sodium ratio(2∶ 1). The combination of tannic acid and cefoperazone sodium-to-sulbactam sodium(1∶ 1) shows synergistic and additive effects and is expected to be a plane of the combination of Chinese and western drugs against CRAB.