Determination of In Vitro Activities of Polymyxin B and Rifampin in Combination with Ampicillin/Sulbactam or Cefoperazone/Sulbactam against Multidrug-Resistant Acinetobacter baumannii by the E-test and Checkerboard Methods

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Cetin E., Tekeli A., Ozseven A. G. , Us E., Aridogan B.

JAPANESE JOURNAL OF INFECTIOUS DISEASES, vol.66, no.6, pp.463-468, 2013 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 66 Issue: 6
  • Publication Date: 2013
  • Doi Number: 10.7883/yoken.66.463
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.463-468
  • Süleyman Demirel University Affiliated: Yes


The aim of this study was to investigate the in vitro activities of polymyxin B (PB) and rifampin (RIF) in combination with ampicillin/sulbactam (AS) or cefoperazone/sulbactam (CS) against 20 multidrug-resistant Acinetobacter baumannii (MDR-AB) isolates by the checkerboard and E-test methods. Fractional inhibitory concentration index (FICI) values were defined as synergy, FICI <= 0.5; additivity, 0.5 < FICI <= 1.0, indifference, 1.0 < FICI < 4.0; and antagonism, FICI >= 4. Synergistic interaction was detected only for the RIF + AS and RIF + CS combinations. While the most frequently detected interaction type for PB + AS or PB + CS combinations was indifference, some showed antagonistic interactions. The detection rate of synergy was significantly higher by the checkerboard than by the E-test method, and the detection rate of indifference was significantly higher by the E-test than by the checkerboard method for RIF + AS combination (P <= 0.0001). In addition, no statistically significant difference was detected between the checkerboard and E-test methods for the detection rates of interaction types for any of the other combinations (P > 0.05), except for PB + CS combination for the detection of additivity (P = 0.018). Owing to the high percentage of synergistic interactions between RIF and AS, we considered this combination as an effective therapeutic option for MDR-AB infections.