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

Abstract

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.

Identification of Blood Culture Isolates Directly from Positive Blood Cultures by Use of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry and a Commercial Extraction System: Analysis of Performance, Cost, and Turnaround Time

“…This compares favorably with data from others using in-house extraction systems for blood culture analysis which have reported correct identification rates ranging from 67 to 100%, with higher success rates for Gram-negative organisms than for Gram-positive organisms (11)(12)(13)(15)(16)(17). Similarly, a recent study by Buchan et al, also using the Sepsityper system, reported that 85.5% of the blood culture isolates tested were identified directly from blood cultures with better performance for Gram-negative organisms (3).…”

Performance of Kiestra Total Laboratory Automation Combined with MS in Clinical Microbiology Practice

“…In staphylococci, rates of correct identification were low (9/35; 25.7%), while for Enterobacteriaceae, the rates were 100% (20/20). This is in accordance with the findings of other groups that used Sepsityper, who found significantly lower identification rates for Gram-positive (42.3-78%) compared to Gram- [16,17]. Direct MS from BCs, regardless of the manufacturer, is labor-intensive and does not replace bacterial culture preparation, since this is still required in order to perform susceptibility tests and exclude bacterial mixtures.…”

A commentary on the role of molecular technology and automation in clinical diagnostics

“…21 Despite this, MALDI-TOF MS analysis can reduce manual workload for medical scientists and improve throughput of laboratory samples. 22 Exemplifying this, previously technically-challenging identification of microorganisms from sputum of cystic fibrosis patients, 8 utilizing multiple selective media and prolonged incubation, may now be completed within 48 hours of sampling. 23 More specifically, a 2012 Canadian study 24 reported a mean reduction in turnaround time of 34.3 hours when definitive identification of isolates directly from blood samples was possible, albeit that this reduction was lower, but still clinically important, at 26.5 hours when incubation was necessary before MALDI-TOF MS could be utilized.…”