Comparison of Meropenem MIC by E Test and VITEK 2 in resistant Pseudomonas and Acinetobacter isolates

Abstract

Pseudomonas aeruginosa and Acinetobacter baumannii cause serious infections in health care institutions. Many isolates are multidrug resistant and sometimes resistant even to meropenem. The minimum inhibitory concentration (MIC) of an antibiotic is useful to decide on specific treatment and several methods of detecting MIC are in current use. Routine application of such methods is cumbersome for clinical laboratories and the newly introduced VITEK 2 automated method is an attractive alternative. The aims of the study were to compare the performance of the E test and the VITEK 2 system in susceptibility testing of resistant strains of P.aeruginosa and A. baumannii to meropenem and to compare the MIC of four different carbapenem antibiotics for P.aeruginosa and A.baumannii. 75 strains of P.aeruginosa and 25 of A.baumanii were selected randomly from the isolate collection of the Princess Alexandra Hospital, Australia. MIC testing using the E test and the VITEK 2 MIC were performed for each isolate according to the manufacturer’s instructions and the CLSI guidelines of June, 2010. MICs obtained by VITEK-2 corresponded closely with those obtained with the E test method. Categorical agreement testing for both organisms was 92% with no major errors and 08% minor errors. We conclude that VITEK 2 is a reliable method to determine MIC to meropenem for P. aeruginosa and A. baumanii. Doripenem sensitivity results can be extrapolated from the meropenem sensitivity results.