Evaluation of the VITEK 2 System for Rapid Direct Identification and Susceptibility Testing of Gram-Negative Bacilli from Positive Blood Cultures

Abstract

This study explores the possibility of combining the BacT/Alert Microbial Detection System with the VITEK 2 system to achieve rapid bacterial identification and susceptibility testing. Direct inoculation of bacterial suspension to the VITEK 2 ID-GNB card and AST-NO09 card was made by differential centrifugation of blood cultures of organisms with gram-negative enteric bacillus-like morphology. A total of 118 strains were investigated; of these, 97 (82.2%) strains were correctly identified to the species level and 21 (17.8%) strains were not identified; by comparing the results with those of the reference method of API identification systems using a pure culture, it was found that no strain had been misidentified. Among the 21 strains with no identification, 13 (61.9%) strains were nonfermenters. The direct-identification reporting time of VITEK 2 was 3.3 h. Direct testing of susceptibility to 11 antibiotics, i.e., amikacin, cefepime, ceftazidime, ciprofloxacin, gentamicin, imipenem, meropenem, netilmicin, piperacillin, piperacillin-tazobactam, and tobramycin, was also performed by using the broth microdilution (MB) method according to the NCCLS guidelines as a reference. After comparing the MICs of the VITEK 2 system with those obtained by the MB method within ؎twofold dilution, it was determined that the 1,067 organism-antibiotic combinations had an overall correct rate of 97.6% (1,041 combinations). The rates of susceptibility to the 11 antibiotics ranged from 88.7 to 100%, respectively. Only two (0.2%) and four (0.4%) combinations of the susceptibility tests gave very major errors (i.e., reported as sensitive by the VITEK 2 system but shown to be resistant by the MB method) and major errors (i.e., reported as resistant by the VITEK 2 system but shown to be sensitive by the MB method), respectively. The reporting time for the direct testing of susceptibility against the 11 antibiotics for 97 blood culture isolates by the VITEK 2 system ranged from 3.3 to 17.5 h. Compared with conventional methods that require 1 or 2 days, this method can make same-day reporting possible and thus permit better patient management.The detection of bloodstream infections is one of the most important tasks performed by the clinical microbiology laboratory. Rapid bacterial identification and susceptibility testing not only improve patient therapy and outcome, but also reduce costs (1,17,18). Both automated blood culture systems and automated systems for identification and susceptibility testing of bacteria have been on the market for a number of years (8). The VITEK 2 system (BioMérieux) is a new automated bacterial identification and susceptibility testing system that uses fluorescence-based technology. Previous studies showed that this system could give reliable identification and susceptibility results with pure bacterial cultures (5, 6, 10). This study explores the possibility of combining these systems to achieve rapid identification and susceptibility testing by direct inoculation from positive blood cultures. MATERIALS AND ME...

Use of Positive Blood Cultures for Direct Identification and Susceptibility Testing with the Vitek 2 System

“…However, two recent publications by Ling et al (15) and Bruins et al (3) which evaluated the direct inoculation of Vitek 2 cards from positive blood culture bottles detected 82 and 93% concordance, respectively, for the direct identification of gram-negative rods. These results are much more favorable than those obtained in our investigation, which was performed in a similar manner.…”

“…However, only a few studies have evaluated the accuracy of identification and the reliability of susceptibility results when cards of the Vitek 2 system are directly inoculated from a positive blood culture (3,15).…”

Evaluation of the Hyplex BloodScreen Multiplex PCR-Enzyme-Linked Immunosorbent Assay System for Direct Identification of Gram-Positive Cocci and Gram-Negative Bacilli from Positive Blood Cultures

“…However, there is no commercial kit for molecular diagnostics of blood cultures yet available and standardization of the assays is lacking. In addition to molecular methods, the Vitek 2 system has recently been evaluated for the identification and susceptibility testing of pathogenic bacteria by direct inoculation from positive BACTEC blood culture bottles and showed promising results (13). However, thus far these evaluations have exclusively used gram-negative bacilli, and problems with the identification of gram-positive cocci have been described (1).…”

Clinical Evaluation of QMAC-dRAST for Direct and Rapid Antimicrobial Susceptibility Test with Gram-Positive Cocci from Positive Blood Culture Bottles

“…These direct AST methods using inoculation from PBCs had quite acceptable results for Gram-negative rods, but not for Gram-positive cocci [8,9,11,12,18]. For higher accuracy of direct AST result for…”

“…For reducing TAT, various researchers have tried to directly process the positive blood culture (PBC) samples without subculture involving overnight culture [7]. AST methods utilizing direct inoculation from PBC had previously been reported with significant agreement rates compared to reference methods [8,9].…”