Article
Rapid identification of bacteria in positive blood culture by matrix-assisted laser desorption ionization-time of flight spectroscopy
Schnelle Erregeridentifikation aus positiven Blutkulturen durch MALDI-TOF
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Authors
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V. Schmidt
- Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne Medical Center, Cologne, Germany
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A. Jarosch
- MVZ Dr. Stein + Kollegen, Department of Medical Microbiology and Infectious Diseases, Mönchengladbach, Germany
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P. Merz
- MVZ Dr. Stein + Kollegen, Department of Medical Microbiology and Infectious Diseases, Mönchengladbach, Germany
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C. Sander
- MVZ Dr. Stein + Kollegen, Department of Medical Microbiology and Infectious Diseases, Mönchengladbach, Germany
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W. Kalka-Moll
- MVZ Dr. Stein + Kollegen, Department of Medical Microbiology and Infectious Diseases, Mönchengladbach, Germany
| Published: | June 2, 2010 |
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Outline
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Blood culture is likely the most significant specimen type used for the diagnosis of bacterial infections, especially for bloodstream infections. Automates perform continuous monitoring of bacterial growth, which ensures quick reports of presumptive identification based on Gram staining to the clinicians in order to adapt presumptive antibiotic therapy. In the present work, we compared three different blood culture bottles in respect to the direct identification of the grown bacteria by matrix-assisted laser desorption ionization-time of flight spectroscopy (MALDI-TOF) mass spectrometry and direct susceptibility testing.
A total of 100 bacterial isolates from clinical blood cultures, representing the most frequent 14 genera and 25 species were examined. Bacteria were inoculated at a defined concentration into BacT/Alert SA (Biomerieux), BacT/Alert FA (Biomerieux), and BD BACTEC™ Plus-Aerobic (Becton Dickinson). Bacteria were extracted from positive blood culture broth by density centrifugation and then subjected to identification by MALDI-TOF and antibiotic susceptibility testing by the VITEK 2 apparatus (Biomerieux). The identification of bacterial isolates by MALDI spectroscopy was compared with biochemical testing of bacterial colonies from agar plates by the VITEK 2 apparatus, and discrepancies were resolved by 16s rDNA sequencing. Antibiotic susceptibility testing by the VITEK 2 from broth extracted bacteria was compared to the respective bacteria grown on agar plates.
Overall correct identification by MALDI-TOF was obtained for the BD BACTEC™ Plus-Aerobic, BacT/Alert SA, and BacT/Alert FA blood culture bottles in 81.7%, 53.9%, and 26.9% respectively, for gram-negative bacteria in 98.7%, 79.5%, and 56.8%, for gram-positive bacteria in 70.0%, 35.0%, and 5.0%, respectively. Lack of identification was observed mostly with viridians streptococci. Overall correct susceptibility testing by VITEK 2 was obtained for the BD BACTEC™ Plus-Aerobic, BacT/Alert SA, and BacT/Alert FA blood culture bottles in 67.3%, 55.8%, and 47.1% respectively, for gram-negative bacteria in 77.3%, 75.0%, and 72.7%, for gram-positive bacteria in 60.0%, 41.7%, and 28.3%, respectively.
Depending on the blood culture bottles used in routine diagnostic procedures MALDI-TOF represents an efficient and rapid method for direct bacterial identification. Direct susceptibility testing from blood culture broth does not provide accurate results.
