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Rapid identification using MALDITOFMS for routine bacterial identification

Abstract number: P1777

Bocher S., Abdul-Redha R.

Objectives: Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is increasingly used as a rapid method for identification of bacteria in the clinical microbiology laboratories. The objective of the present study was to evaluate bacterial identification using MALDI-TOF-MS, Bruker, Germany testing both bacterial isolates and positive blood culture specimens.

Materials and Methods: 90 bacterial isolates from positive routine blood cultures and 97 positive blood culture specimens were used in the evaluation.

Methods: All bacterial isolates and bacteria/fungi from blood cultures were tested by routine laboratory identification methods, prior to testing in by MALDI-TOF MS. Bacterial/fungal isolates: Matrix preparation was performed as recommended by the manufacturer (Bruker Daltonics, www.bdal.com). A small portion of a freshly grown colony was smeared onto the MALDI steel target, whereafter 1mL matrix was added and MALDI-TOF mass spectra were generated using Bruker microflex LT instrument. Positive blood culture specimens: 4 mL blood culture was transferred to gel containing vacuette tube and centrifuged at 2500 rpm for 10 min, hereby separating blood cells and bacteria. Following discard of supernatant, the sediment was washed in 1 mL deionised water. After further centrifugation proteins were extracted from the bacterial cells using formic acid /acetonitrile. 1 mL of the extract was spotted onto the MALDI steel target and MALDI-TOF mass spectra were generated. Bacteria were identified using the Maldi Biotyper 2.0 software, taking into consideration the score, number of identical identifications, distance to next best taxon match, next best taxon match and the automatic evaluation of the obtained identification.

Results: Considering culture and phenotypic characterization the gold standard, 34 genera and 77 different species were represented among 90 isolates and 97 blood culture specimens. Concordant results, different genus and inconclusive identifications are given in the table. CoNS and streptococci accounted for 31 of 55 inconclusive identifications.

Discussion and Conclusion: This study showed a high concordance between routine bacterial identification and identification by MALDI-TOF, especially the species frequently causing bacteraemia. The speed and price seems promising for future routine examination of as well bacterial isolates as clinical specimens, ensuring fast and correct treatment of patients.

Table 1: MALDI-TOF-MS results from blood specimens and isolates

GeneraNo. of strains/positive blood culture specimens examined / genus (species) level
 IsolatesPositive blood culture specimens
Bacteroides3/3 (2) 
Candida1/1 (1) 
Citrobacter4/4 (3) 
Enterobacter1/1 (1) 
Enterococcus4/4 (3)4/4 (3)
Escherichia5/5 (5)5/3 (3)
Haemophilus2/2 (2)1/1
Klebsiella4/4 (4) 
Moraxella5/5 (5) 
Proteus2/2 (2) 
Pseudomonas3/3 (3)5/5 (5)
Salmonella1/11/1 (1)
Staphylococcus9/9 (9)11/11 (11)
Streptococcus15/15 (9)15/13 (2)
Other genera32/17 (11)5/5 (5)
Total nr./genus (species)91/76 (60)73/67 (54)
aIn brackets: no. of identical identification(s) using MALDI-TOF-MS and phenotype characterization, respectively, on genus/species level.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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