Determination of microbial populations with piezoelectric membranes.

The ultrasonic determination of microbial population was carried out by using a new apparatus composed of two piezoelectric membranes. When the apparatus was immersed in a medium containing cells and an arbitrary voltage was charged on a piezoelectric membrane, an output voltage was obtained from the other membrane. The output voltage increased with increasing cell numbers. The linear relationships between the output voltage and microbial populations of Saccharomyces cerevisiae, Bacillus subtilis, and Klebsiella sp. were observed, and the output voltage was reproducible with a relative error of 6%. Furthermore, the cell population of S. cerevisiae in a fermentor could be continuously determined with this apparatus.