A method is disclosed of detecting the presence of an organism in a medium. In some embodiments, the method includes: obtaining a series of optical coherence tomography measurements of a region of the medium processing the series of optical coherence tomography measurements to determine information indicative of translational and rotational motion of an object in the region of the medium identifying the object as organism based on the information indicative of translational and rotational motion of the object and outputting information indication of the presence of the organism.