Evaluation of three sample preparation methods for the direct identification of bacteria in positive blood cultures by MALDI-TOF

Hannah Tanner*, Jason T. Evans, Savita Gossain, Abid Hussain

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

Background: Patient mortality is significantly reduced by rapid identification of bacteria from sterile sites. MALDI-TOF can identify bacteria directly from positive blood cultures and multiple sample preparation methods are available. We evaluated three sample preparation methods and two MALDI-TOF score cut-off values. Positive blood culture bottles with organisms present in Gram stains were prospectively analysed by MALDI-TOF. Three lysis reagents (Saponin, SDS, and SepsiTyper lysis bufer) were applied to each positive culture followed by centrifugation, washing and protein extraction steps. Methods were compared using the McNemar test and 16S rDNA sequencing was used to assess discordant results. Results: In 144 monomicrobial cultures, using ≥2.000 as the cut-off value, species level identifications were obtained from 69/144 (48%) samples using Saponin, 86/144 (60%) using SDS, and 91/144 (63%) using SepsiTyper. The difference between SDS and SepsiTyper was not statistically significant (P = 0.228). Differences between Saponin and the other two reagents were significant (P < 0.01). Using ≥1.700 plus top three results matching as the cut-off value, species level identifications were obtained from 100/144 (69%) samples using Saponin, 103/144 (72%) using SDS, and 106/144 (74%) using SepsiTyper and there was no statistical difference between the methods. No true discordances between culture and direct MALDI-TOF identification were observed in monomicrobial cultures. In 32 polymicrobial cultures, MALDI-TOF identified one organism in 34-75% of samples depending on the method. Conclusions: This study demonstrates two inexpensive in-house detergent lysis methods are non-inferior to a commercial kit for analysis of positive blood cultures by direct MALDI-TOF in a clinical diagnostic microbiology laboratory.

Original languageEnglish
Article number48
Pages (from-to)1-8
Number of pages8
JournalBMC Research Notes
Volume10
Issue number1
DOIs
Publication statusPublished - 18 Jan 2017
Externally publishedYes

Bibliographical note

Funding Information:
This study was internally funded by the PHE Public Health Laboratory Birmingham. The study was carried out as part of normal employment duties of all authors who were all employed by the PHE Public Health Laboratory Birmingham during design of the study and collection, analysis, and interpretation of data and writing the manuscript.

Publisher Copyright:
© 2017 The Author(s).

Keywords

  • Bacteraemia
  • Blood culture
  • Clinical
  • Identification
  • MALDI-TOF
  • Microbiology
  • Sepsis

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