Method for preparing a sample that may contain at least one target microorganism, comprising essentially the following steps: a) placing said sample in a container comprising - a device for the capture and/or concentration of a target microorganism or of a protein from said microorganism, comprising a capture and/or concentration support, said capture support being a porous membrane; - a receptacle with at least two walls, at least one of which is flexible, capable of receiving said sample that may contain at least one target microorganism, said receptacle comprising o an inlet orifice made through one of said walls and allowing the liquid sample contained in the receptacle to pass to the capture and/or concentration device, o an inlet fluid guide, capable of containing a defined sample volume and making it possible to guide said sample volume to said inlet orifice, o at least one means for controlling the volume of sample transferred from the fluid guide to the capture and/or concentration device through said inlet orifice, o an outlet orifice made through one of said walls allowing the sample to pass from the capture and/or concentration device to the receptacle, said capture/concentration device being attached to a wall of the receptacle; b) generating a displacement of all or part of the sample to the fluid guide, c) generating a displacement of a defined volume of the sample from the fluid guide to the capture and/or concentration device through the inlet orifice, d) capturing and/or concentrating, on the capture and/or concentration support, said target microorganism or a protein from said target microorganism contained in the sample, said volume of sample crossing the capture and/or concentration support and then exiting again through the outlet orifice of the receptacle, e) repeating the circulation of the sample in tangential flow through the capture support. a) placing said sample in a container comprising - a device for the capture and/or concentration of a target microorganism or of a protein from said microorganism, comprising a capture and/or concentration support, said capture support being a porous membrane; - a receptacle with at least two walls, at least one of which is flexible, capable of receiving said sample that may contain at least one target microorganism, said receptacle comprising o an inlet orifice made through one of said walls and allowing the liquid sample contained in the receptacle to pass to the capture and/or concentration device, o an inlet fluid guide, capable of containing a defined sample volume and making it possible to guide said sample volume to said inlet orifice, o at least one means for controlling the volume of sample transferred from the fluid guide to the capture and/or concentration device through said inlet orifice, o an outlet orifice made through one of said walls allowing the sample to pass from the capture and/or concentration device to the receptacle, said capture/concentration device being attached to a wall of the receptacle; - a device for the capture and/or concentration of a target microorganism or of a protein from said microorganism, comprising a capture and/or concentration support, said capture support being a porous membrane; - a receptacle with at least two walls, at least one of which is flexible, capable of receiving said sample that may contain at least one target microorganism, said receptacle comprising o an inlet orifice made through one of said walls and allowing the liquid sample contained in the receptacle to pass to the capture and/or concentration device, o an inlet fluid guide, capable of containing a defined sample volume and making it possible to guide said sample volume to said inlet orifice, o at least one means for controlling the volume of sample transferred from the fluid guide to the capture and/or concentration device through said inlet orifice, o an outlet orifice made through one of said walls allowing the sample to pass from the capture and/or concentration device to the receptacle, o an inlet orifice made through one of said walls and allowing the liquid sample contained in the receptacle to pass to the capture and/or concentration device, o an inlet fluid guide, capable of containing a defined sample volume and making it possible to guide said sample volume to said inlet orifice, o at least one means for controlling the volume of sample transferred from the fluid guide to the capture and/or concentration device through said inlet orifice, o an outlet orifice made through one of said walls allowing the sample to pass from the capture and/or concentration device to the receptacle, b) generating a displacement of all or part of the sample to the fluid guide, c) generating a displacement of a defined volume of the sample from the fluid guide to the capture and/or concentration device through the inlet orifice, d) capturing and/or concentrating, on the capture and/or concentration support, said target microorganism or a protein from said target microorganism contained in the sample, said volume of sample crossing the capture and/or concentration support and then exiting again through the outlet orifice of the receptacle, e) repeating the circulation of the sample in tangential flow through the capture support.