Abstract
A completely new approach to diagnose microbial agents at least one day earlier based on mass spectrometric analysis becomes possible in the microbiology laboratory: MALDI TOF: matrix-assisted laser desorption/ionisation time-of-flight. Comparison between results of the new procedure with those obtained by conventional testing is mandatory. 204 clinical isolates grown on agar plates were analysed both, by the MALDI TOF Bruker microflex apparatus and by conventional identification using the VITEK II and API systems, both from bioMérieux. Of the identified isolates, 72 were gram-positive and 130 gram-negative; 2 were yeasts (candida). Concordance was seen with 61/72 (85%) of the Gram-positive bacteria and with 115/130 (88%) of the Gram-negative bacteria. In 27 samples (13.2%), a discrepancy of the species and/or genus was obvious. The discrepancy appeared with 16 gram-negative (12.2%) and with 11 gram-positive germs (15.3%, n.s.). In the latter group, 6 samples showed discordance with Streptococcus pneumoniae (MALDI) and Streptococcus mitis/oralis (conventional identification) constellation. Among gram-negative samples, most differences occurred on the species level only, e.g. Enterobacter cloacae versus Enterobacter kobei. In 5 cases, discordance was major and appeared on the genus level: Enterobacter/Raoultella, Streptococcus/Gemella, Pseumdomonas/Burkholderia, Microbacter/Sphingomonas and Candida/Cryptococcus. The most outstanding difference was Microbacterium arborescens (MALDI TOF) and Sphingomonas paucimobilis (conventional). Molecular biological identification of two Streptococcus mitis group bacteria confirmed the erroneous diagnosis by MALDI TOF of Streptococcus pneumoniae. Good comparability between MALDI TOF analysis and conventional identification procedures (86.8%) but special caution is needed when identifying streptococcal species.
Highlights
In addition to morphological, biochemical microbiological testing analysis along with molecular identification at the DNA and mRNA levels, the matrix assisted laser induced desorption ionisation (MALDI), connected to the time of flight (TOF) channel, is becoming a third diagnostic pillar with strong discriminating power [1,2,3,4]
Molecular biological identification of two Streptococcus mitis group bacteria confirmed the erroneous diagnosis by MALDI TOF of Streptococcus pneumoniae
Thanks to the possibility to ionise and introduce non-volatile molecules into the mass spectrometer, this technique allows for classification and identification of micro-organisms through proteomic fingerprinting and comparison of the spectrometric peak pattern with the MALDI biotype data base which uses the BLAST (Basic Local Alignment Search Tool) procedure; the results are expressed using standard scores based on algorithms for specific identification of the biomarker proteins (SIBP)
Summary
Biochemical microbiological testing analysis along with molecular identification at the DNA and mRNA levels, the matrix assisted laser induced desorption ionisation (MALDI), connected to the time of flight (TOF) channel, is becoming a third diagnostic pillar with strong discriminating power [1,2,3,4]. Only few studies were available which compared bacterial identification obtained on MALDI TOF with those resulting from conventional procedures; In light of this very new time-saving diagnostic tool, many health authorities have yet to approve this technology. At this early stage of MALDI TOF introduction into daily practice, comparison of microbes identified through this expedite procedure to conventional procedures seems mandatory; this paper reports the results of a comparative analysis on 204 clinical specimens for bacteriological analysis provided by MALDI TOF and by conventional BactAlert (API) and Vitek 2 biotype system
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Published Version
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