Carola C Kern, Technische Universität München, Freising, Germany
Co-author(s): Julia Usbeck, Rudi Vogel, and Jürgen Behr Technische Universität München, Freising, Germany
ABSTRACT: The growth of microbial contaminants in
industrially produced beverages can cause turbidity, haze, and
off-flavors resulting in quality loss and often rendering the product
undrinkable. Therefore, rapid and reliable identification and
differentiation of spoilage bacteria is crucial in the beverage industry
to ensure efficient quality control. As traditional methods for
bacterial identification are usually very laborious and time-consuming,
there is a high demand for alternative methods. In this work we present
matrix assisted laser desorption ionization–time-of-flight mass
spectrometry (MALDI-TOF MS) based on the generation of peptide mass
fingerprints, which form a distinctive protein peak pattern, as a rapid,
reliable, and powerful tool for the identification of spoilage bacteria
in beverages. Three strains belonging to the species Lactobacillus brevis, Pediococcus damnosus, and Leuconostoc mesenteroides
were used to optimize sample preparation and MALDI-TOF MS settings to
ensure resulting spectra were of the best achievable quality. Since
MALDI-TOF MS requires a culturing step, and routine quality control
procedures differ vastly in practice, growth conditions such as
culturing time and availability of oxygen and nutrients were varied to
assess their influence on the acquired protein peak pattern.
Additionally, about 50 strains, belonging to the families Lactobacillaceae, Leuconostocaceae, and Acetobacteraceae,
which are frequently encountered in spoilage incidents, were used for
the establishment of a reference spectra database upon optimization of
sample preparation. Data processing was performed using ClinProTools 2.2
and MALDI Biotyper 3.0. Routine identification of bacterial samples was
successfully implemented. Among the tested parameters, neither
culturing time nor availability of oxygen or nutrients impaired
identification of the bacterial isolates on the species level, yielding
only slight differences in spectra. Closer examination of these
differences showed that more than 90% of all spectra could be correctly
assigned to the medium used for culturing, whereas no such correlation
could be established for culturing time and oxygen availability. Taken
together, MALDI-TOF MS allowed differentiation on the species level
regardless of the culture conditions used. The application of specific
environmental conditions resulted in variations in spectra, which were
sufficient to be detected and reliably assigned.
Carola C. Kern
was born in 1984 in Austria. She obtained her master’s degree in
nutritional sciences from the University of Vienna in 2010 and is
currently a Ph.D. student at the Technical University of Munich, where
she’s working on the identification and differentiation of microbial
contaminants in beverages by MALDI-TOF mass spectrometry at the chair of
Technische Mikrobiologie under the supervision of Rudi F. Vogel.
