title: Identification of beer-spoilage bacteria using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.
abstract: Applicability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for identification of beer-spoilage bacteria was examined. To achieve this, an extensive identification database was constructed comprising more than 4200 mass spectra, including biological and technical replicates derived from 273 acetic acid bacteria (AAB) and lactic acid bacteria (LAB), covering a total of 52 species, grown on at least three growth media. Sequence analysis of protein coding genes was used to verify aberrant MALDI-TOF MS identification results and confirmed the earlier misidentification of 34 AAB and LAB strains. In total, 348 isolates were collected from culture media inoculated with 14 spoiled beer and brewery samples. Peak-based numerical analysis of MALDI-TOF MS spectra allowed a straightforward species identification of 327 (94.0%) isolates. The remaining isolates clustered separately and were assigned through sequence analysis of protein coding genes either to species not known as beer-spoilage bacteria, and thus not present in the database, or to novel AAB species. An alternative, classifier-based approach for the identification of spoilage bacteria was evaluated by combining the identification results obtained through peak-based cluster analysis and sequence analysis of protein coding genes as a standard. In total, 263 out of 348 isolates (75.6%) were correctly identified at species level and 24 isolates (6.9%) were misidentified. In addition, the identification results of 50 isolates (14.4%) were considered unreliable, and 11 isolates (3.2%) could not be identified. The present study demonstrated that MALDI-TOF MS is well-suited for the rapid, high-throughput and accurate identification of bacteria isolated from spoiled beer and brewery samples, which makes the technique appropriate for routine microbial quality control in the brewing industry.
authors.affiliation: Laboratory of Biochemistry and Brewing, Faculty of Bioscience Engineering, Ghent University, Valentin Vaerwyckweg 1, B-9000 Ghent, Belgium; Laboratory of Microbiology, Faculty of Sciences, Ghent University, K.L. Ledeganckstraat 35, B-9000 Ghent, Belgium.
authors.forename: Anneleen D
authors.initials: AD
authors.lastname: Wieme
authors.affiliation: Laboratory of Microbiology, Faculty of Sciences, Ghent University, K.L. Ledeganckstraat 35, B-9000 Ghent, Belgium.
authors.forename: Freek
authors.initials: F
authors.lastname: Spitaels
authors.affiliation: Laboratory of Microbiology, Faculty of Sciences, Ghent University, K.L. Ledeganckstraat 35, B-9000 Ghent, Belgium.
authors.forename: Maarten
authors.initials: M
authors.lastname: Aerts
authors.affiliation: Applied Maths N.V., Keistraat 120, B-9830 Sint-Martens-Latem, Belgium.
authors.forename: Katrien
authors.initials: K
authors.lastname: De Bruyne
authors.affiliation: Laboratory of Biochemistry and Brewing, Faculty of Bioscience Engineering, Ghent University, Valentin Vaerwyckweg 1, B-9000 Ghent, Belgium.
authors.forename: Anita
authors.initials: A
authors.lastname: Van Landschoot
authors.affiliation: Laboratory of Microbiology, Faculty of Sciences, Ghent University, K.L. Ledeganckstraat 35, B-9000 Ghent, Belgium. Electronic address: Peter.Vandamme@Ugent.be.
authors.forename: Peter
authors.initials: P
authors.lastname: Vandamme
mesh_terms: D001419:Bacteria / Q000302:isolation & purification*; D001515:Beer / Q000382:microbiology*; D005516:Food Microbiology / Q000379:methods*; D008969:Molecular Sequence Data; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
keywords: Beer-spoilage bacteria; Classifier-based analysis; Identification; MALDI-TOF MS; MLSA; Peak-based cluster analysis