Performance of VITEK 2 in antimicrobial susceptibility testing of Pseudomonas aeruginosa with different mechanisms of beta-lactam resistance

Dipartimento di Patologia, Sezione di Microbiologia, Università di Verona, and Servizio di Microbiologia, Immunologia e Virologia, Azienda Ospedaliera, Verona, Italy

^* To whom correspondence should be addressed. Email: roberta.fontana{at}univr.it.

	Abstract

A total of 78 isolates of Pseudomonas aeruginosa grouped according to the phenotype for ceftazidime and imipenem susceptibility/resistance were used to assess the accuracy of the VITEK 2 system in antimicrobial susceptibility testing. Comparisons were made with an MIC gradient test for piperacillin/tazobactam, ceftazidime, aztreonam, imipenem, meropenem, gentamicin and ciprofloxacin. On the total of 546 isolate/antimicrobial combinations tested the category agreement was 83.6% with 2.0, 1.6 and 12.8% of very major, major and minor errors, respectively. VITEK 2 accuracy was differently influenced by the mechanism responsible for resistance, and interpretation of the results in relation to the phenotype could improve the performance of the system.