In VitroActivities of Combinations of Rifampin with Other Antimicrobials against Multidrug-Resistant Acinetobacter baumannii

Abstract

ABSTRACTThe antimicrobial treatment of multidrug-resistant (MDR)Acinetobacter baumanniiinfections has become a great challenge for medical staff all over the world. Increasing numbers of MDRA. baumanniiinfections have been identified and reported, but effective clinical treatments for them are decreasing. The objective of this study was to investigate thein vitroactivities of combinations of rifampin (an established antimicrobial) and other antimicrobials, including biapenem, colistin, and tigecycline, against 73 clinical isolates of MDRA. baumannii. In total, 73 clinical isolates of MDRA. baumanniiwere collected from two A-level general hospitals in Beijing, and the MICs of rifampin, biapenem, colistin, and tigecycline were determined. The checkerboard method was used to determine the fractional inhibitory concentration indices (FICIs), that is, whether the combinations acted synergistically against these isolates. The MIC50, MIC90, and MICrangeof rifampin combined with biapenem, colistin, and tigecycline against the isolates were clearly lower than those for four antimicrobials (rifampin, biapenem, colistin, and tigecycline) that were used alone. Combinations of rifampin with biapenem, colistin, and tigecycline individually demonstrated the following interactions: synergistic interactions (FICI ≤ 0.5) for 31.51%, 34.25%, and 31.51% of the isolates, partially synergistic interactions (0.5 < FICI < 1) for 49.31%, 43.83%, and 47.94% of the isolates, and additive interactions (FICI = 1) for 19.18%, 21.92%, and 20.55% of the isolates, respectively. There were no indifferent (1 < FICI < 4) or antagonistic (FICI ≥ 4) interactions. Therefore, combinations of rifampin with biapenem, colistin, or tigecycline may be future therapeutic alternatives for the treatment of MDRA. baumanniiinfections.