An evaluation of three processing methods and the effect of reduced culture times for faster direct identification of pathogens from BacT/ALERT blood cultures by MALDI-TOF MS

• Published in: European journal of clinical microbiology & infectious diseases Vol. 31; no. 7; pp. 1575 - 1583
• Main Authors: Loonen, A. J. M., Jansz, A. R., Stalpers, J., Wolffs, P. F. G., van den Brule, A. J. C.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-07-2012; Springer; Springer Nature B.V
• Subjects: Antibiotics; Bacteremia - diagnosis; Bacteria; Bacteria - classification; Bacteria - isolation & purification; Bacteriological Techniques - methods; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Blood; Blood - microbiology; Centrifugation; E coli; Gram-positive bacteria; Humans; Identification; Infectious diseases; Internal Medicine; Laboratories; Mass spectrometry; Medical Microbiology; Medical sciences; Methods; Microorganisms; Pathogens; Scientific imaging; Specimen Handling - methods; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization - methods; Time Factors; France; Netherlands; Blood Culture Bottle; Serum Separation Tube; Positive Blood Culture; Correct Identification Rate; Blood Culture; Infection; Microbiological investigation; Microbiology; Identification; Matrix assisted laser desorption ionization; Method; Blood culture; Mass spectrometry
• ISSN: 0934-9723; 1435-4373
• DOI: 10.1007/s10096-011-1480-y

Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) is a fast and reliable method for the identification of bacteria from agar media. Direct identification from positive blood cultures should decrease the time to obtaining the result. In this study, three different processing methods for the rapid direct identification of bacteria from positive blood culture bottles were compared. In total, 101 positive aerobe BacT/ALERT bottles were included in this study. Aliquots from all bottles were used for three bacterial processing methods, i.e. the commercially available Bruker’s MALDI Sepsityper kit, the commercially available Molzym’s MolYsis Basic5 kit and a centrifugation/washing method. In addition, the best method was used to evaluate the possibility of MALDI application after a reduced incubation time of 7 h of
Staphylococcus aureus
- and
Escherichia coli
-spiked (1,000, 100 and 10 colony-forming units [CFU]) aerobe BacT/ALERT blood cultures. Sixty-six (65%), 51 (50.5%) and 79 (78%) bottles were identified correctly at the species level when the centrifugation/washing method, MolYsis Basic 5 and Sepsityper were used, respectively. Incorrect identification was obtained in 35 (35%), 50 (49.5%) and 22 (22%) bottles, respectively. Gram-positive cocci were correctly identified in 33/52 (64%) of the cases. However, Gram-negative rods showed a correct identification in 45/47 (96%) of all bottles when the Sepsityper kit was used. Seven hours of pre-incubation of
S. aureus
- and
E. coli
-spiked aerobe BacT/ALERT blood cultures never resulted in reliable identification with MALDI-TOF MS. Sepsityper is superior for the direct identification of microorganisms from aerobe BacT/ALERT bottles. Gram-negative pathogens show better results compared to Gram-positive bacteria. Reduced incubation followed by MALDI-TOF MS did not result in faster reliable identification.