Method for classifying the presence or absence of a microorganism in a biological medium

A method for determining the presence or absence of at least one microorganism in a biological medium, said method comprising at least:

• providing an enclosure containing:
• a liquid or semi-solid phase formed in whole or in part of said biological medium capable of containing at least one living form of said microorganism, nutritional elements necessary for proliferation of said microorganism, and an enzymatic substrate that is specific to said microorganism and that can be metabolized into at least one Volatile Organic Compound (VOC) volatile metabolite;
• and
• a gas phase adjacent to said liquid or semi-solid phase,
• exposing at least said liquid or semi-solid phase to conditions that are favorable for said microorganism to metabolize said enzymatic substrate into at least one molecule of said VOC volatile metabolite;
• and
• determining, by optical transduction, the presence or absence of said VOC metabolite, an indicator of the presence of said microorganism;
• wherein:
• said VOC metabolite, if formed, interacts with a nanoporous matrix which has an affinity for said VOC volatile metabolite, said matrix being in a form that is separate from said enzymatic substrate and arranged in the gas phase;
• the detection by optical transduction of a change in the optical properties of said matrix indicates that said matrix interacts with said metabolite;
• and
• VOC is a metabolite specific to the metabolization of the enzymatic substrate and representative of an enzymatic route specific to the microorganism subject of detection.