Rapid and accurate identification of pathogens in positive blood cultures by use of Vitek MS Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry System (MALDI-TOF) after short incubation on a solid medium — ASN Events
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  3. Rapid and accurate identification of pathogens in positive blood cultures by use of Vitek MS Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry System (MALDI-TOF) after short incubation on a solid medium

Rapid and accurate identification of pathogens in positive blood cultures by use of Vitek MS Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry System (MALDI-TOF) after short incubation on a solid medium (#205)

Belinda B Lin 1 , Jenny SJ Wong 1 , Belinda Bombaci 1 , Sasha Jaksic 1
  1. Microbiology, Dorevitch Pathology, Melbourne, Victoria, Australia

MALDI-TOF technology has been practice changing in shortening time to identification of pathogens, particularly bloodstream infections where correct identification and time to correct antimicrobial therapy is critical in optimizing clinical outcomes. 

Method

Blood cultures at Dorevitch Pathology are incubated in BacTalert system (bioMérieux). Eighty five positive blood culture bottles from 53 patients between November 2014 and January 2015 at Western Health, were subcultured as per routine laboratory protocol and also onto a separate chocolate agar plate. Identification of organisms grown on this plate was attempted using MALDI-TOF MS (bioMérieux Vitek MS) at 4, 6, 8 & 24 hours incubation for gram-positive bacteria and after 2, 4, 6, 8 & 24 hours incubation for gram-negative bacteria.

Results

Of 81 monomicrobial positive blood cultures, 61% (28/46) of gram positive bacterial isolates were correctly identified after 4 hours of incubation, 87% (40/46) after 6 hours and 98% (44/46) after 8 hours. 16 of these were Staphylococcus aureus isolates, all 16 (100%) were able to be identified after 4 hours incubation. One Lancefield group C/G streptococcus isolate was misidentified as Streptococcus pyogenes. 47% (17/36) monomicrobial blood cultures with gram negative organisms were correctly identified after 2 hours of incubation and 97% (35/36) after 4 hours of incubation. 4 blood cultures were polymicrobial, MALDI-TOF MS was able to correctly identify 1 of the organisms in all 4 specimens.

Discussion

MALDI-TOF MS is useful in rapid diagnosis of S. aureus bacteremia, allowing early implementation of therapeutic interventions, including selection of anti-Staphylococcal antibiotics, an infectious diseases unit consult and review for possible complications.  MALDI-TOF MS successfully identified 74% (63/85) of isolates in blood cultures after 4 hours incubation, including 95% (35/37) of gram negative pathogens, enabling better informed clinical decisions at an earlier time. Similar principle can be applied to fluid inoculated into blood culture bottles for enrichment cultures for rapid diagnosis. This study was performed in a busy clinical laboratory at an acute care hospital, early MALDI-TOF analysis of blood culture isolates 4 hours after inoculation can be reasonably incorporated into workflow.

  1. Idelevich et al. Clin Microbiol Infect. 2014
  2. Kumar et al. Crit Care Med. 2006
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