*3.4. Identification of Microorganisms by MALDI MS*

Bacterial isolates were stored at −80 ◦C on the Microbank system (VWR, Darmstadt, Germany). Selected colonies were isolated from plates using a sterile pipette tip and applied directly onto a 384-position ground steel target plate (Bruker Daltonics, Bremen, Germany). The samples were immediately mixed with 2 μL of saturated solution of α-cyano-hydroxy cinnamic acid (HCCA, Bruker Daltonics) in 50% acetonitrile (Sigma–Aldrich, Taufkirchen, Germany), supplemented with 2.5% trifluoroacetic acid (Roth, Karlsruhe, Germany). The matrix/sample spots were crystallized by air drying. Spectra of bacterial strains from the KMM collection of our Institute, as well as reference strains from different commercial collections, were used for comparison. Spectra were calibrated with external calibration by *Escherichia coli* DH5 alpha standard and protein calibration standard I (Bruker Daltonics).
