Bactericidal activity and synergy of rifampin alone and in combination against pan-resistant Acinetobacter baumannii

Abstract number: 902_p495

Pachón-Ibañez M.E.


The purpose of this study was to know the bactericidal activity and synergy of rifampin (RMP) alone and in combination with imipenem (IMP) and sulbactam (SB) against two clinical strains of panresistant Acinetobacter baumannii, including resistance to colistin.


MIC and MBC (mg/L) were performed using microdilution method (NCCLS). Time-kill curves were used to evaluate the bactericidal activity and the synergy of antimicrobial combinations (RMP + IMP, RMP + SB and IMP + SB) against the strains 99 and 113. For the time-kill curves antibiotics concentrations used were equivalent to the respective MIC and the Cmax of RMP, IMP and SB obtained in C57BL/6 mice (RMP 25 mg/kg, IMP 30 mg/kg, and SB 60 mg/kg) in time points from 10 to 150 min after a single dose; antimicrobial levels were determined by bioassay method. Antibiotics were considered to be bactericidal when there was a reduction of the original inoculum fr3 log CFU/mL. Synergy was defined as fr2 log decrease in CFU/mL when using the drug combination, relative to the most active component alone.


MIC/MBC: RMP (128/>128) for both strains; IMP (128/>256) for the strain 99 and (256/>256) for the strain 113; SB (>256/>256) for both strains. Cmax: RMP (13.4 mg/L), IMP (16.7 mg/L) and SB (81.5 mg/L). Bactericidal activity: RMP (MIC) was bactericidal for both stains and not with Cmax. IMP was not bactericidal for any of the strains using MIC or Cmax. SB (MIC and Cmax) was bactericidal for the strain 99 and it was not bactericidal against the strain 113. The following combinations were synergistic: RMP + IMP (MIC and Cmax) and RMP + SB (MIC and Cmax) for both strains.


The combination of RMP plus IMP or SB is synergistic against selected clinical strains of panresistant A. baumannii. These results suggest that these combinations may be useful in the treatment of experimental infections caused by this agent.


Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Location: Oxford, UK
Presentation type:
Back to top