In vitro activities of several antimicrobials alone or in combination against MDR Acinetobacter baumannii isolated from intensive care unit

Abstract number: P1162

López-Fabal F., González-Romo F., Culebras E., Picazo J.J.

Objective:Acinetobacter baumannii has become an important hospital-acquired pathogen. Carbapenems have been the agents of choice for serious Acinetobacter infections, but unfortunately, outbreaks of A. baumannii resistant to all antimicrobials except the polymyxins, have been reported. This fact creates demand on the application of some combinations of older antimicrobials on that species. The objective of this study was to assess the in vitro activity of 27 antibiotics against MDR strains of A. baumannii isolated from ICU, and determine whether combinations of colistin with another antibiotics act synergistically against these strains.

Methods: 32 non-repetitive isolates of A. baumannii were included in the study. Isolates were recovered from 21–12–2006 to 18–2–2007. Antibiotic susceptibility testing was determined by the broth dilution method according to the CLSI recomendations.

Etest with imipenem and imipenem plus EDTA were used to check metallo-b-lactamase (MBL) production. We also used cefotaxime (CT)/ cefotaxime + clavulanic acid (CTL) and cefepime (PM)/ cefepime + clavulanic acid (PML) E-test® for testing ESBL production in MDR A. baumannii isolates.

Four strains of A. baumannii were selected for the synergy study. Levels of synergistic activity for colistin combined with doxycicline, rifampicin, imipenem, meropenem and tigecycline were evaluated using the checkerboard method.

Results: All the isolates showed a high level of resistance to all b-lactam antibiotics tested. With the exception of colistin (0% of resistance) there were no antibiotics with good activity against these isolates. Of the other antibiotics tested, tigecycline shows the best activity with 1.5 mg/L of CMI90 value. MBL and ESBL were present in 32 and 0 isolates respectively. All the isolates showed the same susceptibility results, suggesting an outbreak presence.

The results of the checkerboard synergy analysis for MDR strains A. baumannii shown partial synergy or indifferent results.


1Susceptibility pattern revealed presence of MDR A. baumannii outbreak in ICU.

2Metallo-b-lactamases were responsible of carbapenems resistance.

3In studies of synergy, the effect of the combination treatment is unclear, although the possibility of a beneficial effect cannot be excluded

4Tigecycline and colistin seem like the best option to treat these multirresistant bacteria.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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