MALDI-TOF Mass Spectrometry: A Method for the Detection of Bacterial Contamination in Platelet Concentrates Yasmine Chetouane (Presenter) IHU méditerranée infection Presenter Bio: Yasmine, doctoral student in the 3rd year of the thesis.She works in the research unit on Microbes Evolution Phylogeny and Infections (MEPHI), on the Mediterranean infection site in Marseille. She is working on a new approach to detect bacterial contamination in platelet concentrates before transfusion in collaboration with the French Blood Establishment of Marseille, led by Prof. Jacques Chiaroni.

Authors: Yasmine Chetouane* (1), Pierre Gallian (2), Jacques Chiaroni (3), Didier Raoult (1), Laurence Camoin-Jau (1)
1-Aix-Marseille University, IHU Mediterranean infection, Research Unit Microbes Evolution Phylogeny and Infections (MEPHI). 2- Etablissement Français du Sang (EFS) La Plaine Saint-Denis, France 3- Aix-Marseille University, CNRS, EFS, ADES UMR 7268, Marseille, France

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been recently introduced in microbiological laboratories for the identification of microorganisms with proteomics approaches. Here, we investigate the use of MALDI-TOF MS by means of a Microflex MS (MALDI Biotyper-Bruker Daltonik, Germany) for the rapid, cheap and reliable detection and identification of bacterial contamination in Platelets Concentrates (PCs). We have demonstrated the stability and reproducibility of the spectrum over time and whatever the blood group of PCs. Also, we have compared the sensitivity and the specificity of the BACTEC cultivation method to the MALDI-TOF.

Introduction

The use of blood products is associated with a very high level of safety today. However, bacterial risks still exist, more particularly for Platelet Concentrates (PCs) given their preparation and storage conditions.

Various methods for detection bacterial contamination in PCs bags have been developed or suggested. Today, although many techniques for detecting bacterial contamination in PCs are proposed, there is currently no rapid, sensitive and specific reference method.

To our knowledge, this is the first time that MALDI-TOF has been used to detect any bacterial contamination in PCs which are considered a complex environment.

Methods

35 whole bags of PCs were contaminated in order to obtain a final concentration of 102 CFU/bag at the time of inoculation. Seven strains were tested. After inoculation, PCs were left under agitation for 24 hours at room temperature. At the end of this period, 8 ml of contaminated PCs were taken from a BACTEC bottle and in parallel 1 ml of PCs was incubated for 8 hours at 37°C with agitation in the presence of trypticase soy broth in order to be analyzed by MALDI-TOF. These contaminated samples underwent a step of debridement with saponin followed by extraction with formic acid and acetonitrile.

The spectra were analyzed by the MALDI Biotyper software version 3.0 (Bruker Daltonics). Each bag was analyzed 30 times, for a total of 1050 tests using MALDI-TOF technology (Bruker Daltonics).

Results

The analysis of the samples by MALDI TOF allowed for the detection and early identification at 8 hours of all bacterial strains tested as well as an identification of all the bacteria tested.

For the remaining bacteria, the detection time by BACTEC was significantly longer than 8 hours (mean: 10h41, n = 25, p value <0.005, T-test). Moreover, a period of 24 hours after the time to detection is necessary to correctly identify the strain by MALDI-TOF. In this case, depending of the strain, 46 or 56 hours are necessary for final identification.

Conclusions & Discussion

We have demonstrated the possibility of detecting bacteria in the PCs with MALDI TOF, whatever the strain and very quickly by obtaining the results for the detection at 8 h after 24 h of agitation, with sensitivity and specificity comparable to that of the BACTEC method.