Rapid identification and susceptibility testing using the VITEK® 2 system using culture fluids from positive BacT/ALERT® blood cultures
Jiunn-Rong Chen, Shih-Yi Lee, Bing-Heng Yang, Jang-Jih Lu
Department of Neuroscience, Tzu-Ai General Hospital, Hsilo, Yulin; and Division of Clinical Pathology, Department of Pathology, Tri-Service General Hospital and National Defense Medical Center, Taipei, Taiwan
Received: March 27, 2007 Revised: May 1, 2007 Accepted: May 8, 2007
Background and purpose:
In order to reduce the turnaround time for laboratory diagnosis of bacteremia, the efficacy of identification and antimicrobial susceptibility testing using samples taken directly from positive BacT/ALERT® standard aerobic and standard anaerobic blood culture bottles was evaluated.
160 positive blood culture bottles were examined and incubated at 35°C in 5% carbon dioxide for 4-24 h, and an aliquot of the culture fluid was Gram stained. Samples containing Gram-negative bacilli were inoculated on VITEK® 2 ID-GNB (identification-Gram-negative bacilli) and AST (antimicrobial susceptibility testing)-GN04 cards, and those containing Gram-positive cocci were inoculated on ID-GPC (identification-Gram-positive cocci) and AST-P526 cards. The same samples were also examined by the standard method, involving subculture from positive BacT/ALERT standard blood culture bottles.
Eighty seven of 97 Gram-negative bacilli (89.7%) and 21 of 63 Gram-positive cocci (33.3%) were correctly identified to the species level. For antimicrobial susceptibility testing, the direct method had an overall error rate of 5.4% for Gram-negative bacilli, with 0.9% very major, 0.9% major, and 3.6% minor discrepancies compared to the standard method. The overall error rate in antimicrobial susceptibility testing for the 13 Staphylococcus spp. was 10.3%, with 6.0% very major, 2.6% major, and 1.7% minor discrepancies.
These data suggest that VITEK 2 cards inoculated with samples taken directly from positive Bact/ALERT blood culture bottles would provide acceptable identification and antimicrobial susceptibility testing results for Gram-negative bacilli, but not for Gram-positive cocci. Compared to the standard method, the direct method would reduce turnaround time by at least 24 h.
Bacterial typing techniques; Gram-positive bacteria; Gram-negative bacteria; Microbial sensitivity tests; Reagent kits, diagnostic
J Microbiol Immunol Infect. 2008;41:259-264.