A system is disclosed for agitating multiple specimen containers each containing a sample and a growth medium. The system includes a plurality of racks. The racks have a plurality of receptacles, each of which is adapted for holding a specimen container. The racks include a first rack oriented in a first direction and a second rack oriented in a second direction different from the first direction. The system also includes a rotating turret having a frame holding the racks. The frame is rotatable about an axis, wherein the rotating turret operates to rotate the racks about the axis to an access position, e.g., where a user may access the specimen containers. The system also includes an agitation assembly coupled to the racks. The agitation assembly rocks the racks back and forth thereby agitating specimen containers held by the racks. In one configuration, the system is incorporated into an automated instrument detecting whether a microbiological agent is present in the specimen container. In another configuration, the system is incorporated into an automated instrument identifying or characterizing the microbiological agent.