Automatic tracking and analysis system for free-swimming bacteria

Bacterial swimming is mediated by flagella. The rotary activity of this organelle is controlled by a signal transduction pathway which integrates several stimuli from the surrounding environment. The study of the flagellar rotary motor and the transduction pathway system associated with its control frequently requires the analysis of the swimming behavior of several hundred independent cells. Simple eye analysis of such large numbers of bacteria is difficult and tedious. Automated specific purpose commercial tracking systems may be expensive or locked for extended user developments. In this paper, we describe an automatic basic bacteria tracking method which can be easily implemented by using a general-purpose image analyzer. The method obtains dynamic information of free-swimming bacteria from a recorded digital video film. The tracking system reconstructs simultaneously the trajectories of all cell bodies in the film by matching its center of mass from frame-to-frame, resulting in individual cell paths. Dynamic information of the bacterial swimming behavior is obtained: average run speed, maximum and minimal speed, total average speed, average run time, average stop time, stop frequency, interval moving frequency and the distributions of runs, stops, speeds, distances and accelerations. An average correlation factor of 0.99 has been obtained for manual and automated results.