Method for determining the sensitivity of a bacterial strain to a viral strain of bacteriophages, the method comprising: a) preparing a sample, this comprising bringing bacteria, of the bacterial strain, into contact with bacteriophages, each bacteriophage belonging to the same viral strain, the bacteria being either in a liquid medium, or in an agar medium; b) placing the sample between a light source and an image sensor, the light source emitting a light wave in an emission spectral band comprised between 500 nm and 600 nm, the image sensor lying in a detection plane; c) illuminating the sample using the light source and acquiring at least one image of the sample, with the image sensor, in the emission spectral band, the image sensor being: - either arranged in a lensless imaging configuration, no magnifying or image-forming optics being placed between the sample and the image sensor; - or arranged in a defocused imaging configuration, an optical system, i.e. a lens or objective, being placed between the sample and the image sensor, the optical system defining an object plane and an image plane, the object plane being offset from the detection plane or the image plane being offset from the sample; d) on the basis of each acquired image, determining a sensitivity of the bacterial strain to the viral strain of the bacteriophages, the method being such that: - in step a), the bacteria and the bacteriophages are mixed in an aqueous solution; - step c) comprises acquiring at least two images, at successive measurement times; - step d) comprises determining a light intensity detected by all or part of the image sensor, in each image respectively acquired at each measurement time (t), such that the bacterial strain is considered to be: • hardly or not sensitive to the viral strain of the bacteriophages when the detected light intensity decreases between two successive measurement times; • or sensitive to the viral strain of the bacteriophages when the detected light intensity does not decrease or increases between two successive measurement times. a) preparing a sample, this comprising bringing bacteria, of the bacterial strain, into contact with bacteriophages, each bacteriophage belonging to the same viral strain, the bacteria being either in a liquid medium, or in an agar medium; b) placing the sample between a light source and an image sensor, the light source emitting a light wave in an emission spectral band comprised between 500 nm and 600 nm, the image sensor lying in a detection plane; c) illuminating the sample using the light source and acquiring at least one image of the sample, with the image sensor, in the emission spectral band, the image sensor being: - either arranged in a lensless imaging configuration, no magnifying or image-forming optics being placed between the sample and the image sensor; - or arranged in a defocused imaging configuration, an optical system, i.e. a lens or objective, being placed between the sample and the image sensor, the optical system defining an object plane and an image plane, the object plane being offset from the detection plane or the image plane being offset from the sample; - either arranged in a lensless imaging configuration, no magnifying or image-forming optics being placed between the sample and the image sensor; - or arranged in a defocused imaging configuration, an optical system, i.e. a lens or objective, being placed between the sample and the image sensor, the optical system defining an object plane and an image plane, the object plane being offset from the detection plane or the image plane being offset from the sample; d) on the basis of each acquired image, determining a sensitivity of the bacterial strain to the viral strain of the bacteriophages, - in step a), the bacteria and the bacteriophages are mixed in an aqueous solution; - step c) comprises acquiring at least two images, at successive measurement times; - step d) comprises determining a light intensity detected by all or part of the image sensor, in each image respectively acquired at each measurement time (t), such that the bacterial strain is considered to be: • hardly or not sensitive to the viral strain of the bacteriophages when the detected light intensity decreases between two successive measurement times; • or sensitive to the viral strain of the bacteriophages when the detected light intensity does not decrease or increases between two successive measurement times. • hardly or not sensitive to the viral strain of the bacteriophages when the detected light intensity decreases between two successive measurement times; • or sensitive to the viral strain of the bacteriophages when the detected light intensity does not decrease or increases between two successive measurement times.