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Updated: Apr 23, 2026
Antimicrobial Synergy Testing by the Inkjet Printer-assisted Automated Checkerboard Array and the Manual Time-kill Method
Published on: April 18, 2019
Meropenem/colistin synergy testing for multidrug-resistant Acinetobacter baumannii strains by a two-dimensional
Alex van Belkum1, Diane Halimi2, Eve-Julie Bonetti3
1Microbiology R&D, Microbiology Unit, bioMérieux SA, La Balme Les Grottes, France alex.vanbelkum@biomerieux.com.
Objectives:
Precise assessment of potential therapeutic synergy, antagonism or indifference between antimicrobial agents currently depends on time-consuming and hard-to-standardize in vitro chequerboard titration methods. We here present a method based on a novel two-dimensional antibiotic gradient technique named Xact™.
Methods:
We used a test comprising a combination of perpendicular gradients of meropenem and colistin in a single quadrant. We compared test outcomes with those obtained with classical chequerboard microbroth dilution testing in a study involving 27 unique strains of multidrug-resistant Acinetobacter baumannii from diverse origins.
Results:
We were able to demonstrate 92% concordance between the new technology and classical chequerboard titration using the A. baumannii collection. Two strains could not be analysed by Xact™ due to their out-of-range MIC of meropenem (>128 mg/L).
Conclusions:
The new test was shown to be diagnostically useful, easy to implement and less labour intensive than the classical method.
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