Abstract: A method for detecting and enumerating viable microorganisms in a sample suspected of containing said microorganisms comprising: (1) contacting said sample with a cell nutritive resource and a cellular proliferation inhibitor, (2) contacting said sample with at least one fluorescence labelled oligonucleotidic probe able to specifically hybridise at least one portion of ribosomal nucleic acids of said microorganisms, (3) detecting and quantifying the fluorescent signal, in which the microorganisms are of the species Legionella pneumophila and in which the cellular proliferation inhibitor is selected from the group consisting of ciprofloxacin and cephalexin.