Evaluation of MicroScan WalkAway and Vitek 2 for determination of the susceptibility of extended-spectrum b-lactamase-producing Escherichia coli and Klebsiella pneumoniae isolates to cefepime, cefotaxime and ceftazidime

Results: The proportion of isolates classified as susceptible to cefepime and ceftazidime with the CLSI and EUCAST guidelines was 35.0% versus 2.3% for cefepime (P,0.001) and 21.8% versus 8.2% for ceftazidime (P,0.001), respectively, and the susceptible isolates were mainly the CTX-M-9 group or SHV-type ESBL producers. All of the isolates were resistant to cefotaxime. Against the total of 220 ESBL-producing isolates, using the CLSI (EUCAST) criteria, very major/major error rates of MicroScan and Vitek 2 were as follows: 1.9%/20.8% (1.8%/20.0%) and 27.4%/0% (12.2%/0%) for cefepime and 2.6%/8.3% (1.2%/0%) and 4.5%/0% (2.3%/0%) for ceftazidime, respectively. The very major error rates of MicroScan and Vitek 2 with cefotaxime were 0.9% and 1.4%, respectively. The errors were mainly major errors for MicroScan and very major errors for Vitek 2.