Evaluation of VITEK 2 rapid identification and susceptibility testing system against Gram-negative clinical isolates

A total of 281 strains of miscellaneous members of the family Enterobacteri aceae, Pseudomonas aeruginosa, and other gram-negative bacteria were evalua ted by use of identification tests with the VITEK 2 system (bioMerieux) and an API identification system (bioMerieux). A total of 237 (95%) strains we re correctly identified to the species level. Only six (2.1%) strains were misidentified, and eight (2.8%) strains were not identified. Among 14 strai ns with discrepant identifications, 8 (57.1%) strains were nonfermenters. T he susceptibilities of 228 strains to 11 antibiotics including amikacin, ne tilmicin, tobramycin, gentamicin, ciprofloxacin, imipenem, meropenem, cefta zidime, cefepime, piperacillin, and piperacillin in combination with tazoba ctam were tested with the VITEK 2 AST-No. 12 card and by the broth microdil ution (MB) method, according to NCCLS guidelines, as a reference. For the 2 ,508 organism-antibiotic combinations, the rates at which duplicate MICs co rrelated within I dilution ranged from 84.2 to 95.6%. Only 13 (0.5%) and 10 (0.4%) of the susceptibility tests gave major errors (resistant with the V ITEK 2 system but sensitive by the MB method) and very major errors (sensit ive with the VITEK 2 system but resistant by the MB method), respectively. Both VITEK 2 ID-GNB (an identification system) and VITEK 2 AST-No. 12 (a su sceptibility testing system) card systems gave rapid, reliable, and highly reproducible results.