Evaluation of the in vitro activity of ampicillin-sulbactam and cefoperazone-sulbactam against A. Baumannii by the broth disk elution test

To evaluate the in vitro activity of ampicillin-sulbactam and cefoperazone-sulbactam against A. baumannii using the broth disk elution testing, a total of 150 A. baumannii isolates were collected from across China between January 2019 and January 2021, including 51 carbapenem-susceptible and 99 carbapenem-resistant isolates. Broth disk elution (BDE) and the broth microdilution (BMD) method were performed for all strains. The concentration range of the BDE was 10/10 mu g/mL, 20/20 mu g/mL, and 30/30 mu g/mL for ampicillin-sulbactam, and 37.5/15 mu g/mL, 75/30 mu g/mL, 112.5/45 mu g/mL, and 150/60 mu g/mL for cefoperazone-sulbactam, respectively. Compared with BMD, the BDE results of ampicillin-sulbactam and cefoperazone-sulbactam showed a categorical agreement of 83.3% (125/150) and 95.3% (143/150), with minor errors of 16.7% (25/150) and 4.7% (7/150), respectively. No major error or very major errors were detected. The sensitivity differences by BDE of carbapenem-resistant A. baumannii (CRAb) to different concentrations of ampicillin-sulbactam showed statistically significant (p < 0.017), while those to cefoperazone-sulbactam at 37.5/15 <mu>g/mL, 75/30 mu g/mL, and 112.5/45 mu g/mL were significant (p < 0.008). However, no significant difference in sensitivity was observed between 112.5/45 <mu>g/mL and 150/60 mu g/mL (p > 0.008). In conclusion, the BDE is a reliable and convenient method to detect the in vitro activity of cefoperazone-sulbactam against A. baumannii, and the results could serve as a clinical reference value when deciding whether or not to use high-dose sulbactam for the treatment of A. baumannii infections.