Same Day MALDI-TOF Identification of Bacteria from Positive Blood Culture Bottles: Evaluation of two Methods — ASN Events
  1. Schedule
  2. Poster Session A
  3. Same Day MALDI-TOF Identification of Bacteria from Positive Blood Culture Bottles: Evaluation of two Methods

Same Day MALDI-TOF Identification of Bacteria from Positive Blood Culture Bottles: Evaluation of two Methods (#203)

Kerry Varettas 1 , David Siebert 2
  1. South Eastern Area Laboratory Services, BEVERLEY PARK, NSW, Australia
  2. Infection Management Services, Princess Alexandra Hospital, Brisbane, Queensland, Australia

Introduction

The advent of MALDI-TOF mass spectrometers has increased the pressure in clinical microbiology laboratories to identify bacteria faster than ever before. In this study, two methods that enabled the same day identification of bacteria from positive blood culture bottles (BacT/Alert FAN Plus, bioMérieux) by MALDI-TOF (Bruker) were evaluated in parallel with the standard overnight culture method.

Method

Using a ‘short-incubation’ method, 2 drops of blood culture broth was inoculated onto a chocolate agar plate, without streaking, and incubated for 4-hours (35°C CO2). MALDI-TOF testing was performed from the inoculum.

Alternatively, the ‘pellet’ method used a Vacuette gel tube inoculated with 5ml of blood culture broth. The tube was centrifuged at 2000 rpm for 15-min, the supernatant discarded and the pellet used to inoculate the MALDI target plate using a cotton swab.

Only organisms commonly isolated in this laboratory with identification to the species level (MALDI-TOF score values of ≥2) were included in this evaluation. Streptococci sp identified as Streptococcus pneumoniae and mixed Gram-stain results were also excluded from the data.

Results

During the period 30/09/2014 – 09/04/2015, 376 bottles were included in the evaluation. The short incubation and the pellet method respectively identified 89.4% & 64.6% of Enterobacteriaceae, 42.9% & 0% Pseudomonas aeruginosa, 81.0% & 19.0% S.aureus, 17.9% & 9.0% of coagulase-negative Staphylococci, 41.2% & 23.5% of Streptococci sp and 57.1% & 35.7% of Enterococcus sp. 

Discussion

The ‘short incubation’ method was able to identify a greater number of isolates to the species level than the pellet method and in agreement with the routine overnight culture protocol. This method is low cost, fast and easy to incorporate into the existing workflow and requires minimal blood culture broth processing.

Conclusion

The ‘short incubation’ method is able to provide same day identification of commonly isolated bacteria from positive blood culture bottles using MALDI-TOF testing

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