Validation of the VITEK2 and the Advance Expert System with a collection of Enterobacteriaceae harboring extended spectrum or inhibitor resistant beta-lactamases

The susceptibility testing accuracy of the VITEK2 system and the ability of the Advance Expert System (AES) to provide interpretive readings were eval uated against 86 extended spectrum (ESBL) and 6 inhibitor-resistant-TEM (IR T) beta -lactamases producing Enterobacteriaceae clinical isolates. VITEK2 MICs of 12 beta -lactams were compared with those obtained by the standard NCCLS microdilution technique. The overall essential agreement (+/- 1 log d ilution) was 87.8%. Discrepancies were mainly observed with cefepime (30.3% of total number of discrepancies), ceftazidime (21.2%), and cefotaxime (15 .1%). MIC discrepancies were slightly higher in CTX-M- (14.4%) than in TEM- (12.5%) or SHV- (11.9%) type ESBL producers and were rare in IRT producers (1.4%). Overall interpretive agreement was 92.5% and minor, major, and ver y major errors were 5.4%, 1.7%, and 2.1%, respectively. The AES was able to identify an ESBL phenotype in 85 out of 86 isolates (98.8%) and an IRT phe notype in all 6 isolates harboring these enzymes, thus reducing very major errors to 0.9%. The VITEK2 system, in conjunction with the AES software, is a reliable tool for detection of ESBL or IRT producing Enterobacteriaceae isolates. (C) 2001 Elsevier Science Inc. All rights reserved.