Purpose: To evaluate in vitro activities of β-lactam antibiotics alone and in combination with sulbactam at different ratios against Acinetobacter baumannii  clinical strains from China.
Methods: A total of 300 clinical isolates of A. baumannii  were collected from 29 hospitals across China in 2018. Susceptibility to common antibiotics was assessed, and β-lactamase genes were detected. In vitro activity of ampicillin, cefoperazone and imipenem was tested alone and in combination with sulbactam at the ratios of 2:1, 1:1, 1:1.5, 1:2, 1:2.5 and 1:3.
Results: High resistant rates for common antibiotics were observed except tigecycline and polymyxin B. Among carbapenem-resistant A. baumannii , 97.3% isolates harbored bla _OXA-23. MIC₅₀ and MIC₉₀ values for sulbactam were 32 mg/L and 64 mg/L, respectively. High resistant rates for ampicillin, cefoperazone and imipenem were observed (92.3%, 93% and 85.3%, respectively). A stepwise increase in the ratio of sulbactam to partner β-lactam antibiotics led to a stepwise decrease in the MICs and a stepwise increase in the susceptible rates. The susceptible rates for imipenem-sulbactam 1:3, ampicillin-sulbactam 1:3 and cefoperazone-sulbactam 1:3 reached 16.3%, 58.3% and 91%, respectively.
Conclusion: The increasing proportion of sulbactam could enhance antimicrobial activities of imipenem-sulbactam, ampicillin-sulbactam and cefoperazone-sulbactam combinations against A. baumannii  clinical strains in China, with cefoperazone-sulbactam as the most potent compound.
Keywords: sulbactam, ampicillin, cefoperazone, imipenem, Acinetobacter baumannii