Abstract

A hybrid three-axis laser Doppler velocimeter (LDV) system has been set up in our laboratory. The system can monitor the motion of microbes in a larger volume and in a nearly natural environment. A computer is used to collect and process the data only when one microbe swims within the measuring volume. We can then obtain a FFT spectrum that represents exactly the motion signature of this particular microbe. The ambiguity caused by multiscattering among two or more microbes can be avoided. By using this new system and FFT spectrum analysis, a feature vector related to the size of a microbe, its average translational velocity, its rotation or wobbling, and its flagellum motility is obtained. Such a vector is a good criterion for distinguishing different species based on a weighted average maximum likelihood algorithm. We have successfully identified several species under a controlled environment. It thus becomes possible to automatically identify known microbes. In addition, this system can be used to discover or search for unexpected microbes in a situation where the concentration is low.

© 1992 Optical Society of America