Comparison of three automated systems (BD Phoenix, MicroScan WalkAway and VITEK 2) for detecting imipenem resistance in Acinetobacter baumannii

Abstract number: P853

Kulah C., Aktas E., Comert F., Ozlu N., Akyar I., Ankarali H.

Objectives: Carbapenems are considered the gold standard treatment for multidrug resistant Acinetobacter baumannii infections, however, resistance to this agent has been reported increasingly. Reliable susceptibility testing results remains a critical issue for the clinical outcome for these patients. Automated systems are currently used in many clinical laboratories. This study was organised to evaluate the accuracies of three automated susceptibility testing methods for testing Acinetobacter baumannii against imipenem.

Methods: One hundred twelve selected isolates of Acinetobacter baumannii collected between January 2003 and December 2006 were tested to confirm imipenem susceptibility results. Bacterial isolates were identified according to conventional bacteriological techniques and confirmed by API 20 NE (bioMerieux, France). Strains were tested against imipenem by broth dilution, disk difusion, Etest (AB Biodisk, Sweden), BD Phoenix (Becton Dickinson), MicroScan WalkAway (Dade Behring) and VITEK 2 (bioMérieux) automated systems. Data were analysed by comparing the results from each test method to those produced by the reference broth microdilution (BMD) test performed using in-house prepared panels.

Results: MicroScan performed true identification of all A. baumannii strains while VITEK 2 unidentified one strain, and Phoenix unidentified two strains and misidentified two strains. The BMD testing showed that 25 strains were susceptible to imipenem while 87 were resistant All other test systems in the study produced errors when A. baumannii was tested against imipenem. Etest showed the best performance with only two minor error (1.8%). VITEK 2 produced eight minor errors(7.2%). BD Phoenix produced three major errors(2.8%). Disk diffusion produced two very major errors (1.8%) and three major errors (2.7%). MicroScan showed the worst performance in susceptibility testing with 28 very major errors (25%) and 50 minor errors (44.6%).

Conclusions: Testing difficulties for imipenem do exist in susceptibility testing systems. Reporting errors can have serious implications for the clinical outcome for patients. We suggest clinical laboratories using automated systems for routine use should consider using a second, independent antimicrobial susceptibility testing method to validate imipenem susceptibility.

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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