The invention relates to a medium for detecting and/or identifying microorganisms present in a sample, comprising a culture medium and at least one substrate that can be hydrolysed to a labelled product by at least a first enzyme not free in the sample, and specific for the microorganisms, characterized in that it also comprises at least one inhibitor of at least a second enzyme, different from the first enzyme or identical to it, but free in said sample and not originating from a microorganism. The present invention also finds a preferred application in the field of biomedical diagnosis or in food microbiology, and more particularly in bacteriology and mycology.