A device and method for detecting microorganisms in a specimen by culturing the specimen in a sealable specimen container with a culture medium and detecting microorganisms in the specimen-by measuring changes in pressure within the container caused by their metabolic activity during culturing. Pressure changes are measured using a sensor having a deformable section in communication with the container and a piezoelectric apparatus, such that the piezoelectric apparatus is deformed by changes in pressure within the specimen container and an electrical signal is produced by the deformation. The electrical signal is processed to detect any change in the rate of change of pressure, and thus detect the growth of microorganisms.