Comparative evaluation of Vitek 2 identification and susceptibility testing of Gram-negative rods directly and isolated from BacT/ALERT-positive blood culture bottles

Abstract

TheperformanceofVitek2wasevaluatedforthe identification and susceptibility testing of Gram-negative bacilli directly frompositivebloodculturesbottles.Direct inoculation of the positive blood cultureswith theVitek cards ID-GN andAST-NO58was comparedwith the standard inoculationmethod based on the sub-culture of the positive blood culture to agar. A total of 142 blood cultureswereincludedinthestudy;ofthose,119werefrom patients’ clinical samples, while 23 were artificially preparedwith strains showing different mechanisms of resistance. A total of 136 (95.8%) strainswere correctly identified to the species level, only 2 (1.4%) weremisidentifiedand4 (2.8%)werenot identified. Susceptibility results were available for all isolates tested against 17 antibiotics, thus, resulting in a total of 2,414 isolate/antimicrobialcombinations.Theerrorratewas2.8%(67/2,414) overall;0.6%(14/2,414)verymajorerrors, 0.1%(3/2,414) major errorsand2.1%(50/2,414)minor errors.Thedirect method detected 88.5%(22/25) of the strains producing extended-spectrumbeta-lactamases (ESBLs). The susceptibility agreement among the added strains with ESBL, AMPchyperproduction, resistance toceftazidime, carbapenemsandcefepimewasveryhigh.Direct identificationand susceptibility testing gave rapid and reliable results, reducingby24h the turnaround timeof themicrobiology laboratory.