Abstract: The present invention relates to a method for detecting resistant microorganisms to a therapeutic agent in a biological sample, comprising the following steps: a. inoculate the said sample, uncultured, on a first tube with, and on a second tube without, at least one therapeutic agent; preferentially further including at least one lysing agent and/or a buffer, and/or a suitable culture medium, or put the sample on a separation serum tube; and incubated it; b. add to both tubes a fluorescent marker; c. perform a fluorescence analysis for obtaining one or more fluorescence or growth parameters for each of the two tubes; wherein the microorganisms resistant phenotype of the biological sample to said therapeutic agent is obtained by comparing the one or more fluorescence parameters between the two tubes.