Preparing live microbial samples and microorganisms for subsequent mass spectrometric measurement and evaluation

Method for the preparation of microorganisms for a subsequent mass spectrometric measurement, comprising the steps of:

• (a) providing a flat sample support having a plurality of sample spots;
• (b1) culturing the microorganisms in a liquid nutrient medium, which comprises originally clear culture broth, in a vessel away from the flat sample support;
• (b2) transferring the cultured microorganisms to, and depositing them on, a first one of the sample spots in a droplet of the liquid nutrient medium in which they have been cultured;
• (c) maintaining the flat sample support for a predetermined resting period to allow a microorganism deposit to form on the first sample spot;
• (d) removing residual liquid of the droplet of nutrient medium after the predetermined resting period to expose the microorganism deposit;
• (e) preparing the first sample spot for a desorbing ionization;
• (f) transferring the sample support into a desorption ion source of a mass spectrometer, generating ions from the prepared first sample spot and acquiring a corresponding mass spectrum;
• and
• g) comparing the mass spectrum with a reference data set to determine at least one characteristic of the microorganisms in a phenotypic test.