Protein denaturation piezoelectric frequency shift method for determination of microorganisms

A protein denaturation piezoelectric frequency shift method was used to det ermine the number of bacteria based on the influence of bacterium metabolis m on milk. Compared with methods presented earlier based on coagulation of the medium it was more rapid, as less than half an hour was needed for dete ction after a preincubation of several hours. The proposed method was used to determine Escherichia coli. The end-point frequency shift was linearly r elated to the logarithm of the initial number of E, coli in the range 1.4 X 10(2)-1.4 X 10(5) cells.ml(-1). Calibration graphs of E. coli and Micrococ cus lysodeikeicus were compared; the results may be helpful for the qualita tive analysis of various bacteria. Finally, changes in milk freshness was m onitored by this method. (C) 1999 Academic Press.