Method for classification of micro-organisms of a biological sample comprising micro-organisms in one of at least two classes on the basis of spectral data comprising a MALDI MS spectrum or a MALDI TOF MS spectrum, the method comprising the steps of: creating a database for use in classification of a sample in one of at least two classes on the basis of spectral data, wherein the creating of the database comprises: a) obtaining at least two sets of first spectra for use as reference spectra, each set corresponding to a class of micro-organisms, wherein each set comprises spectra of reference samples of micro-organisms belonging to a same class wherein reference spectra are obtained from droplets each comprising a single micro-organism of said class; b) determining for each of the reference spectra the value of the same at least one quantity related to a spectral feature included in a selected one of said spectral data by applying a predetermined function or operation to each of the reference spectra; and c) for each set of reference spectra, associating a probability to different values of said at least one quantity on the basis of the determined values, and constructing a probability density function from said quantity values and associated probabilities; and wherein the classification of said micro-organisms comprises: d) obtaining a spectrum from droplets each comprising a single micro-organism from the sample and determining the value of the same at least one quantity of this spectrum; and e) calculating on the basis of the probability density functions obtained from the database and the value of the quantity for the obtained spectrum for each of said at least two classes a probability that the sample belongs to that class. creating a database for use in classification of a sample in one of at least two classes on the basis of spectral data, wherein the creating of the database comprises: a) obtaining at least two sets of first spectra for use as reference spectra, each set corresponding to a class of micro-organisms, wherein each set comprises spectra of reference samples of micro-organisms belonging to a same class wherein reference spectra are obtained from droplets each comprising a single micro-organism of said class; b) determining for each of the reference spectra the value of the same at least one quantity related to a spectral feature included in a selected one of said spectral data by applying a predetermined function or operation to each of the reference spectra; and c) for each set of reference spectra, associating a probability to different values of said at least one quantity on the basis of the determined values, and constructing a probability density function from said quantity values and associated probabilities; and a) obtaining at least two sets of first spectra for use as reference spectra, each set corresponding to a class of micro-organisms, wherein each set comprises spectra of reference samples of micro-organisms belonging to a same class wherein reference spectra are obtained from droplets each comprising a single micro-organism of said class; b) determining for each of the reference spectra the value of the same at least one quantity related to a spectral feature included in a selected one of said spectral data by applying a predetermined function or operation to each of the reference spectra; and c) for each set of reference spectra, associating a probability to different values of said at least one quantity on the basis of the determined values, and constructing a probability density function from said quantity values and associated probabilities; and wherein the classification of said micro-organisms comprises: d) obtaining a spectrum from droplets each comprising a single micro-organism from the sample and determining the value of the same at least one quantity of this spectrum; and e) calculating on the basis of the probability density functions obtained from the database and the value of the quantity for the obtained spectrum for each of said at least two classes a probability that the sample belongs to that class. d) obtaining a spectrum from droplets each comprising a single micro-organism from the sample and determining the value of the same at least one quantity of this spectrum; and e) calculating on the basis of the probability density functions obtained from the database and the value of the quantity for the obtained spectrum for each of said at least two classes a probability that the sample belongs to that class.