An Algorithm for Automated Bacterial Identification Using Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Abstract

An algorithm for bacterial identification using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is being developed. This mass spectral fingerprint comparison algorithm is fully automated and statistically based, providing objective analysis of samples to be identified. Based on extraction of reference fingerprint ions from test spectra, this approach should lend itself well to real-world applications where samples are likely to be impure. This algorithm is illustrated using a blind study. In the study, MALDI-MS fingerprints for Bacillus atrophaeus ATCC 49337, Bacillus cereus ATCC 14579T, Escherichia coli ATCC 33694, Pantoea agglomerans ATCC 33243, and Pseudomonas putida F1 are collected and form a reference library. The identification of test samples containing one or more reference bacteria, potentially mixed with one species not in the library (Shewanella alga BrY), is performed by comparison to the reference library with a calculated degree of association. Out of 60 samples, no false positives are present, and the correct identification rate is 75%. Missed identifications are largely due to a weak B. cereus signal in the bacterial mixtures. Potential modifications to the algorithm are presented and result in a higher than 90% correct identification rate for the blind study data, suggesting that this approach has the potential for reliable and accurate automated data analysis of MALDI-MS.

Bacterial analysis by MALDI-TOF mass spectrometry: An inter-laboratory comparison

“…Data between laboratories were then compared in the following manner. Sixty replicate spectra were used to create a fingerprint within each laboratory following the procedure described in [3,13]. Thirty additional spectra collected within each laboratory were compared to all three laboratory fingerprints using an algorithm for automated bacterial identification [3]étoéestimateétheédetectionérateéoféE.…”

“…The m/z values for mass spectral peaks and the patterns with which they are observed provide very specific and unbiased analysis, as they indicate molecular weights of true components of the sample. Bacterial cells have been identified by comparing MALDI-TOF spectra obtained from cultured bacterial cells and simple microbial mixtures against a library of known MALDI-TOF spectral fingerprints obtained from intact bacterial cells [3,4] or from comparison with masses predicted from a proteomic database [5,6]. The proteomic approach has been demonstrated to correctly identify bacteria from spectra originating at different laboratories [5], however, this approach is currently suffering from an incomplete protein database for many of the organisms that are of interest.…”

Einsatz der Matrix-Assisted Laser Desorption/ionisation-Time of Flight Massenspektrometrie (MALDI-TOF MS) in der mikrobiologischen Routinediagnostik/Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) in clinical microbiological routine diagnostics

“…Dieses massenspektrometrische Verfahren hat prinzipiell das Potenzial, die klassischen biochemischen Differenzierungsverfahren in der mikrobiologischen Diagnostik abzul ö sen, da es wesentliche Vorteile wie sehr kurze Analysenzeiten, einfache Bedienung und Automatisierbarkeit bei geringen Verbrauchskosten, sowie hohe Sensitivit ä t und Spezifi t ä t in sich vereint [1] . [7,8] . Dies ergibt eine sehr kurze Umsatzzeit bis zum positiven Ergebnis.…”

MALDI-TOF MS: Its Application in the Clinical Laboratory and a Paradigm Shift in Clinical Microbiology

“…Current algorithms allow the entire computational analysis to be performed in near real time [4,5]. Therefore, if only one sample is to be measured, it can be pro- …”